Learn French: J'ai presque oublié mon cauchemar.

In French compound tenses like the passé composé, short or common adverbs like presque, bien, and déjà are placed right between the helping verb (ai) and the past participle (oublié).

Could I put presque at the end of the sentence instead?

No, placing it at the end sounds unnatural in French. Short adverbs of degree or quantity need to stay between the two verb parts. Adverbs that go at the end of a sentence are usually adverbs of time, like hier.

I see mon before cauchemar. Does that mean the word is masculine?

Exactly. Cauchemar is a masculine noun. It is a good word to memorize because it does not end in a typical masculine pattern, and learners often mistakenly try to spell it with an extra E at the end.

If I wanted to use a longer adverb like complètement, would it still go in the middle?

Yes! While the rule strictly applies to short adverbs, many longer adverbs ending in -ment also step right between the helping verb and the past participle. You would say J'ai complètement oublié mon cauchemar.