One day in law school (well, actually at "Law Park"), I was rigging up my 6.0 meter sail for a great day of spring windsurfing. I mentioned to another sailor that I was suppose to be in Con. Law I at that given hour. I didn't know it at the time, but he was an attorney. He said something to the effect of: "I almost flunked Con. Law."
[Before anyone gets their undies in a bundle, remember we're talking about "Constitutional Law" liberal UW Madison style. I wouldn't be too proud about passing that one.]
Heck, my wife first saw me in my 3L (EDIT: oops, 2L, sorry honey [:I] ) year of Civ. Pro. II. Well, the first two weeks or so. Then I skipped and prolly did more windsurfing and mountain biking. Ultimately I took the class pass/fail (trust me, it was a cliffhanger!!) and met her after an exam at the Union at 10:30 a.m. sucking down suds. We both have jobs in a very competitive market and are doing pretty well.
Point being, the goal of law school should be to graduate from law school and nothing more. My wife basically stumbled into her practice and it's been wonderful for her. I suffered to get to where I'm at, but I love the work.
Only worry about grades if you need grades to get to where you want to go. But, in most of those cases, keep in mind that you'll work your heart out for 7 years and then be looking for a new job if you're not on partnership track.
There are many options out there for you. Don't worry about this. When you do "fall into" your niche, you'll have stuff to bounce back from there too, so this is good practice.
Good luck.
EDITED to add that you do actually have to successfully complete law school to get a JD. See the core class requirement pass/fail cliffhanger noted above. [;)] But once you get that first job it's experience and how well you do. That IMHO is the real test. I've seen book smart attorneys wash out whereas most of the better courtroom attorneys have been independent thinking on their feet type of people. All depends on what you want to do.
EDITED second time -- noted in text. No new girlfriends my 3L year! My wife is one of the better divorce lawyers in town. I'm sure she'd take my AR15's just to spite me. [:D]