Quite frankly, even if your diagnostic test says that you don't need LSAT prep, you NEED LSAT prep, regardless. Your actual score will be around 5-10 points lower than your diagnostic, and even a few points can make a huge difference in scholarship potential. After you get your LSAT, compare it with your target schools. Personally, since I needed some large scholarships, I applied mainly to schools which I was above the 75th Percentile in both LSAT and GPA. Luckily for you, LSAT heavily outweighs GPA, so you have a huge opportunity to almost undo 3 years of not caring about school. Then, start visiting, wait for the offers, and accept one.