corner twists

So I just got a stickerless new island phoenix today, and it came rather loose. (oh and I'm brand new at cubing and can't solve a cube yet) As I was scrambling it, I think I flipped one of the corners in a different rotation than it was. Does this matter? Can I fix it? How can I tell...

Hi everyone! Today I was practicing some OH and got a few corner twists especially during specific algs for OLL. Normally, I just correct the corner twist with both hands, but what would actually happen in a real competition scenario when you need to twist it back? It's nearly impossible...