Dopuszczalne są obie formy. Najczęściej spotykaną (i uznawaną przez niektórych, a właściwie większość, za jedyną poprawną) jest oczywiście "were", ale w nieformalnych możemy spotkać się również z "was".

Pozdrawiam! :-)

Jest tak jak pisze wojtek.j , stosuje sie if was and if were, z tym ze if was w unreal conditionals jest zastosowane nieprawidlowo.
Ale wyczytalem, ze jest roznica pomiedzy if was and if were
if was mozemy zastosowac, gdy cos moglo sie zdarzyc

https://www.grammarly.com/blog/conditional-sentences-was-instead-of-were/

If the verb in the if clause is “to be,” use “were,” even if the subject of the clause is a third person singular subject (i.e., he, she, it).

If I was a rich man, I would make more charitable donations. (incorrect)
If I were a rich man, I would make more charitable donations. (correct)

If he was here right now, he would help us. (incorrect)
If he were here right now, he would help us. (correct)

Remember, though, that this exception applies only to unreal conditionals—that is, situations that do not reflect reality. (Hint: unreal conditionals often contain words like “would” or “ought to.”) When you’re talking about a possibility that did happen or might be true, use “was” and “were” as you normally would.

If I were rude to you, I apologize. (incorrect)

If I was rude to you, I apologize. (correct) - "Jezeli bylem nieuprzejmy dla ciebie, przepraszam cie" - moglo tak sie zdarzyc