When forming hypothetical sentences, remember to respect the so-called (the law of tenses and moods combinations). In the case of Type 3 hypotheticals, it requires you to have the past perfect subjunctive in the “if clause.”
Therefore, be careful never to put a verb in the conditional straight after se(if).
❌ Se saremmo andati a Roma, avremmo visto il Colosseo.
✅ Se fossimo andati a Roma, avremmo visto il Colosseo.
If we had gone to Rome, we would have seen the Colosseum.