My opinion is that it is quite obsessive.
Two issues:
1) You’re 3/4 into your HS career. Replacing one B with in A isn’t going to move the needle much in terms of your GPA. I’m going to estimate you have 30-36 units of classes done. Changing the grade of one of those units just doesn’t have a big effect since that grade has to try to move the other 29-35 units.
2) Even if you were to be able to change your class rank, the entire class is 3/4 into the marathon. What would your rank move to? Maybe 15th to 14th? 8th to 7th? The point I’m making is you’re probably not going to move much in terms of ranking anyway. If you’ve got 100 kids in your class, then going from 15th to 14th still gets you in the top 15% of your class. Going from 9th to 8th still gets you in the top 10% of your class. You didn’t tell us your class rank so for all I know you may be still in the running for Val or Sal. Really at this point, it’s hard to move significantly in class ranking unless your class is separated by thousandths decimal places.
You’d be better off getting in shape for the CFA or doing other things that may improve your app like volunteer work. Work on your essays. The common app (which you will probably use for your plan B, C, and D schools) open up in August but the essay prompts are out there. Work those essays as well as those for the SAs, noms, and ROTC.
If you get into a SA, then this will be the last summer you’ll get with significant amount of free time. Enjoy it. Go on vacation. Relax. Hit senior year hard so you’re not letting off the gas.
Good luck.