Op researched schools well - those are the very schools s/he should apply to as a low income international needing 100% financial aid: those are both need blind and full need schools.
Your stats are fine.
You may want to take the English literature subject test and a foreign language sat subject (if you studied French or Spanish for instance) or either one to show Academic versatility (excellence in more than science).
My recommendation is to apply ED to Amherst. Deadline is November 1 so you only have three days to write the essays, not sure how feasible that is. If you’re in All Saints’ Day Holiday you may have the full three days. Start NOW actually. You have till Midnight EST which would be early morning on the 2nd. Work on essays, send them.
Wrt the Polish scale, 2=C, 3=B, 4= A-, 5=A/A+ (6 would be equivalent to Academic awards in the US).
Generally speaking, don’t lower yourself. It doesn’t work in the US . For instance, a 5.1 in the science stream is “nationally ranked” level, worthy of Warsaw institute. In the US it’d be a humble brag to say somethibg like this (ie., You pretend to be humble but you’re really trying to show off) even though I’m guessing you’re being “European modest”. You can’t just brag, though - you must seriously evaluate how good you are in comparison to other Polish students. You must not downplay your achievements and you must evaluate them honestly.