Language / How can I perfect my Polish grammar? [10]

Hi I'm a polish american teenager and while I always speak Polish at home my parents never really practiced the grammar with me since I was very little so I am constantly being corrected when I speak polish lol Most of the time I actually knew the way to say something but I forgot at that moment and well I want to become as fluent a person living in poland. Where could I go about doing this? if I had to guess i'd say I'm 4th or 5th grade level with grammar.

Also a side question, I have a weird heavy accent when I speak polish thats not even american I don't know what it is it might be something close to ukranian (my father was half ukranian) And I'd like to work on fixing that because I'm very embarrassed whenever I visit my family in Poland and sometimes they don't understand what I'm saying because of the accent. My parents were from Warszawa