Truly and honestly, past acedemic performance is a good indicator of future acedemic performance. While this is not always true and people overcome acedemic struggles, it's important for you to know and to know that medical school is going to be the MOST difficult thing you've ever done. Nursing school
would probably be the second most difficult thing you've ever done.
I'm honestly being sincere and not mean when I say this, but do you know if you'll get accepted into nursing school with your past acedemic performance of a 50% on a final exam? I would talk to the acedemic counselors at some schools
that you're thinking about attending to see if they can do a transcript evaluation for you.
Nursing school and college in general is a WHOLE lot harder than high school, so you're going to have to start getting serious and work really hard on your general education prerequisite classes. Pay particular attention in math and science classes and definitely pay attention in your English classes as you'll probably be writing a lot of papers in college and probably in nursing school too.
With all that said, nursing school is most likely going to either be a waste of time and not prepare you for medical school (the method of training is completely different and you'll still be lacking many prerequisites required for application to medical school) or you'll absolutely love nursing and won't want to do medical school. Nursing and medicine are too drastically different to compare.