Se te enganares na quantidade de baunilha, o bolo fica com um gosto estranho.

Because after se meaning if, Portuguese often uses the future subjunctive when talking about a possible future situation.

• se te enganares = if you make a mistake / if you get it wrong
• not se te enganas, which sounds more like a general or habitual statement

This is very common in European Portuguese:

• Se tiveres tempo, liga-me. = If you have time, call me.
• Se fores cedo, apanhas o comboio. = If you go early, you catch the train.

So in your sentence, enganares is the correct form for a future possibility.

Here enganar-se means to make a mistake, to get something wrong, or to be mistaken.

So:

• enganar = to deceive / trick
• enganar-se = to be mistaken / to make a mistake

In this sentence, it means making a mistake with the amount of vanilla.

Examples:

• Enganei-me nas contas. = I made a mistake in the calculations.
• Enganaste-te no número. = You got the number wrong.

The verb here is reflexive: enganar-se.

The te is the reflexive pronoun for tu:

• eu engano-me
• tu enganas-te
• ele/ela engana-se

In clauses with se, the pronoun usually comes before the verb in standard Portuguese:

• Se te enganares...

So te means yourself, but in English we usually do not translate it literally. We just say if you make a mistake.

Because se triggers proclisis, which means the object/reflexive pronoun moves before the verb.

So you get:

• Se te enganares...

not:

• Se enganares-te...

This is a very important Portuguese pattern. Words like se, não, quem, quando, porque, and some others often pull pronouns in front of the verb.

Literally, it means in the quantity of vanilla.

But in natural English, we would usually say:

• with the amount of vanilla
• about the amount of vanilla
• in the amount of vanilla

Here na is a contraction of:

• em + a = na

And quantidade de baunilha means amount of vanilla.

So:

• enganar-se na quantidade de baunilha = to make a mistake in/with the amount of vanilla

Sometimes yes, but enganar-se em / enganar-se em algo or enganar-se no/na... is the more natural pattern here.

• enganar-se na quantidade = to get the quantity wrong

Using com is less natural in this sentence.

So for this specific structure, na quantidade de baunilha is the better choice.

Both are possible, but they are slightly different in feel.

• o bolo fica com um gosto estranho = the cake ends up with / comes out with a strange taste
• o bolo tem um gosto estranho = the cake has a strange taste

Ficar com often suggests the result of something:

• You used the wrong amount of vanilla,
• and as a result, the cake turns out tasting strange.

So fica com works very well because the sentence is about consequence.

Both relate to taste/flavour, but they are not always used in exactly the same way.

• gosto often means taste
• sabor often means flavour

In this sentence:

• um gosto estranho = a strange taste

That sounds natural and idiomatic.

Very roughly:

• gosto can focus more on the taste itself
• sabor can sound a bit more like the flavour profile

But in everyday language, there is overlap, and both words are common.

Because in Portuguese, adjectives often come after the noun.

So:

• um gosto estranho = a strange taste

This is the normal order.

If you put the adjective before the noun, sometimes the meaning or tone changes, but in this case the standard and natural phrasing is:

• um gosto estranho

Portuguese often uses the present tense in both parts of an if sentence when talking about general consequences or likely results.

So:

• Se te enganares..., o bolo fica...

This means something like:

• If you make a mistake..., the cake ends up tasting strange

It is a normal structure in Portuguese:

• future subjunctive after se
• present indicative in the result clause

Example:

• Se chover, ficamos em casa. = If it rains, we stay home.

Yes. The form te and the verb enganares show that the sentence is addressing tu.

Clues:

• te = reflexive pronoun for tu
• enganares = future subjunctive form of tu

If it were você, the sentence would be:

• Se se enganar na quantidade de baunilha, o bolo fica com um gosto estranho.

That sounds more formal and less common in many everyday situations in Portugal, where tu is very common.

Yes, it sounds natural in European Portuguese.

It is a normal, idiomatic sentence, with several very typical EP features:

• se + future subjunctive: se te enganares
• reflexive pronoun placement: te
• natural expression: enganar-se na quantidade
• result expression: fica com um gosto estranho

A native speaker of European Portuguese would understand it immediately and find it natural.

In this sentence, se primarily means if.

However, in real use, Portuguese if sentences can sometimes imply something quite likely, depending on context. So the feeling may occasionally be close to if/when in English.

Still, the direct meaning here is:

• If you make a mistake with the amount of vanilla, the cake gets a strange taste.

If you specifically wanted when, Portuguese would normally use quando:

• Quando te enganas na quantidade de baunilha...

But that would suggest something more habitual or expected, which is not the idea here.