Apunta la combinación, no vaya a ser que olvidemos el número.

Yes. Here apunta is the tú affirmative imperative of apuntar.

• apuntar = to write down / note down
• apunta = write it down / note it down

So Apunta la combinación means Write down the combination.

For regular -ar verbs, the tú affirmative command looks like the él/ella/usted present form:

• apuntar → apunta
• hablar → habla
• comprar → compra

So even though apunta can also mean he/she points or you point in formal speech depending on context, here it is clearly a command.

In Spanish, the definite article is used much more often than in English. So la combinación is perfectly natural where English often says simply the combination or even just combination depending on context.

Here la combinación means something like:

• the combination
• usually the combination to a lock, safe, etc.

Spanish often prefers the article when talking about a specific known thing.

Yes. In this sentence, la combinación refers to the number combination for a lock, safe, or similar device.

Depending on context, Spanish might also use words like:

• el código
• la clave
• el número

But la combinación is completely natural when talking about a lock combination.

No vaya a ser que is a fixed expression meaning:

• in case
• lest
• for fear that
• so that it doesn’t happen that
• more naturally in English here: in case we forget the number

It introduces a possible unwanted situation.

So:

• Apunta la combinación, no vaya a ser que olvidemos el número.
• Write down the combination, in case we forget the number.

It is a very common Spanish structure for expressing precaution.

Because vaya is the present subjunctive form of ir, and in the expression no vaya a ser que, that subjunctive form is part of the fixed construction.

Breakdown:

• ir → vaya
• ser stays in the infinitive here: ser
• que introduces the possible event

So literally, very roughly, it is something like:

• let it not turn out that...
• may it not be that...

But learners should usually treat no vaya a ser que as one expression rather than trying to translate each word separately.

Because no vaya a ser que triggers the subjunctive.

After this expression, Spanish uses the subjunctive because it refers to something:

• possible
• uncertain
• feared
• not presented as a fact

So:

• no vaya a ser que olvidemos el número
• in case we forget the number

Compare:

• Olvidamos el número. = We forget / are forgetting the number. → statement of fact
• No vaya a ser que olvidemos el número. = in case we might forget the number → possible situation, so subjunctive

Because olvidar is a regular -ar verb, and the present subjunctive for nosotros ends in -emos.

Conjugation of olvidar in the present subjunctive:

• yo olvide
• tú olvides
• él/ella/usted olvide
• nosotros olvidemos
• vosotros olvidéis
• ellos/ellas/ustedes olviden

So olvidemos means that we forget.

It refers to the speaker and at least one other person. In context, it usually means:

• you and I
• or all of us involved

So the sentence implies something like:

• Write down the combination, in case we forget the number.

Even though the first verb is a command to one person (apunta = you write it down), the second part includes the speaker too (olvidemos = we forget).

That shift is completely natural.

Yes, but it would not mean exactly the same thing.

• Apunta la combinación, para que no olvidemos el número. = Write down the combination so that we don’t forget the number.

This sounds more like purpose.

• Apunta la combinación, no vaya a ser que olvidemos el número. = Write down the combination in case we forget the number.

This sounds more like precaution against a possible problem.

So both are possible in some contexts, but no vaya a ser que emphasizes the risk or fear of something going wrong.

Yes. No sea que is another common expression with a very similar meaning:

• Apunta la combinación, no sea que olvidemos el número.

This also means:

• Write down the combination, in case we forget the number.

Both are correct. In many contexts, no vaya a ser que can sound a bit more idiomatic or a bit more emphatic, but both are common and natural.

Because the sentence has two parts:

1. Apunta la combinación — the command
2. no vaya a ser que olvidemos el número — the reason/precaution

The comma helps separate the main instruction from the caution that follows. This is normal punctuation in Spanish.

Yes. It sounds natural in Spain.

A speaker in Spain might also say similar things like:

• Apunta la combinación, por si se nos olvida el número.
• Apunta el número, no vaya a ser que luego se nos olvide.
• Anota la combinación, no sea que la olvidemos.

Your sentence is idiomatic and correct, especially in a slightly careful or cautionary tone.

Very little in this context.

• apuntar = to note down / write down
• anotar = to write down / jot down / record

Both can work here:

• Apunta la combinación
• Anota la combinación

In everyday use, both are natural. Sometimes anotar feels slightly more explicitly like to write something down, while apuntar is very commonly used in Spain with that same meaning.