Please tell me what to do

I'm really scared of making any more mistakes and not being able to graduate college on time. I'm at my third year of working towards my four year degree in Environmental Science, and it's getting really hard right now. I already failed Chemistry, and I don't have a lot of time to get all of my science credits to graduate. 

Can someone please tell me how I should work? I'm really insecure and I never push myself to study or practice science problems at home. I haven't been taking notes at all during my Biology class, I just guess whenever I have homework. I only passed my first exam with a 65 from pure guesswork, and I don't think I could pass like this.

Is it worth it to start studying and taking notes now even though I'm in the middle of the semester? I didn't do this before cause I hate being away from my phone. I'm sorry. I'm very lazy.