Противень был слишком горячим, и мне пришлось поставить его на полотенце.

Противень is a baking tray, oven tray, or sheet pan—the flat metal pan you use for baking in the oven.

So in this sentence, it is the hot tray that needed to be set down on a towel.

Even though противень ends in -ь, it is a masculine noun.

That matters because other words in the sentence agree with it:

• был = masculine past tense of быть
• его = it/him referring back to a masculine noun

So the sentence treats противень as masculine all the way through.

Because the subject is противень, and противень is masculine singular.

In the past tense, Russian verbs agree with the subject in gender and number:

• masculine: был
• feminine: была
• neuter: было
• plural: были

So Противень был... = The tray was...

Here горячим is the instrumental case form of горячий.

After быть in the past tense, Russian can use a predicate adjective in different ways, and the instrumental is very natural here when describing the tray’s state at that moment:

• Противень был слишком горячим = The tray was too hot

You may also hear nominative adjectives after быть in some contexts, but горячим is a very standard and natural choice here.

Слишком means too in the sense of excessively or more than is okay.

So:

• слишком горячим = too hot

This is different from очень, which means very:

• очень горячий = very hot
• слишком горячий / горячим = too hot

In this sentence, слишком shows that the heat caused a problem.

This is a very common Russian way to say I had to.

• мне is dative: to me
• пришлось is the past tense of прийтись, used impersonally here

Literally, it is something like it fell to me or it turned out that I had to.

So:

• мне пришлось поставить его... = I had to put it...

This construction is especially common when circumstances force the action.

Because пришлось is being used impersonally.

In this structure, there is no normal grammatical subject like я. Instead, Russian uses:

• мне = the person affected
• пришлось = a fixed impersonal past form, usually neuter singular

So it does not agree with мне. The idea is not I came/arrived, but rather it became necessary for me.

Yes, you could, but the nuance is different.

• мне пришлось поставить его... = I had to put it down because the situation made it necessary
• я должен был поставить его... = I was supposed to / was obliged to put it down

In this sentence, the tray was too hot, so the need comes from the situation. That makes мне пришлось the more natural choice.

Because поставить is perfective, and here the sentence refers to one completed action: setting the tray down.

• поставить = to put/set down once, as a completed act
• ставить = to put/set repeatedly, habitually, or as an ongoing process

Since the speaker had to do one specific thing with the tray, поставить fits better.

Его means it here, referring back to противень.

Because противень is masculine, the pronoun used is the masculine form:

• его = it / him

Grammatically, this is the accusative form, because it is the direct object of поставить.

A useful detail: with an inanimate masculine noun, the noun itself often looks the same in nominative and accusative, but the pronoun still changes:

• противень → still противень as a direct object
• but он → его

Here на means onto, so it normally takes the accusative case with a verb of motion like поставить:

• поставить на полотенце = put onto a towel

The confusing part is that полотенце has the same form in nominative and accusative singular, so you do not see a visible change.

Compare with a word where the forms are different:

• поставить на стол = put onto the table (accusative)
• лежать на столе = be lying on the table (prepositional)

With полотенце, the form happens to stay полотенце, but the case is understood from the verb and meaning.

Because Russian has no articles.

So противень can mean:

• a tray
• the tray

And полотенце can mean:

• a towel
• the towel

The listener figures out which one is meant from context. In this sentence, English might naturally say the tray and a towel or the towel, but Russian does not need separate words for that.