Question: I took the SAT I in March and did really well (Math-790, Verbal-800, Writing-740) but, before I got my scores back, I signed up to retake it in May. I've already paid the fee and I think that if I take it again I could do better, but I wanted to know if it would hurt me to do worse.
Colleges typically use your best scores from each section of the SAT, even if they're from different testings, so it can't hurt to re-take the tests. Sure, if you do egregiously worse (very unlikely) then colleges will see the new scores as well as the old ones, but they'll really only pay attention to your highest numbers.
However, since you did so well the first time around, it's certainly not necessary to take the tests again. Alternatively, according to the College Board, even though the May test is just a week away, it isn't too late for you to decide to take SAT IIs this month instead of the SAT I. In order to do so, you can just show up at your test center as planned but tell the proctor that you've switched to the Subject Tests. If you don't feel prepared to do that, you can also notify the College Board that you won't be testing at all on May 7th. They will then apply the fee you've paid to any SATs you take down the road.