I want to become a criminal lawyer SO bad! I want this so bad?

my parents tell me I cant become a lawyer,,

I do understand why, they believe I wont make it. I was a 65-70 % average student. BUT I didn't take school seriously because I ddint care, was immature, now that I am older, I wish I had different mentality. BUT maybe that's why they say im not that type, because I totally understand that a typical lawyer is not someone who has a "unserious" nature like me? if that even justifies my doubt ? should I go after my dream profession or get it out of my head and pursue something "realistic" . I mean I do lack a lot of knowledge from high school...but I have free 6 months before I start college(social work)so I can use that time to re-educate myself.im thinking of buying textbooks about:history of cananda,introduction to law,books that will improve my critical/analytical skills,books to improve my vocabulary. those topics are crucial and more important for criminal lawyer than math/science, so ill leave them out. im just scared if..what if I just wont get into law school no matter how hard I try.its kind of like this, theres ppl that are mathematicians only because math comes natural to them, and theres ppl that admire, want to become mathematicians but will blow their brains out so like..why bother if that's just not...you and you don't have that gift, u kno what I mean? I just don't know what to do, because those students that do take school seriously have that attitude towards life & are the ones that become doctors/lawyers etc.