…don’t worry if your other scores drop a little.
That’s what superscoring is for.
So if you scored a 700 in Math and a 670 in Writing on the first test and are retaking to get your Critical Reading score above 650, you do not need to have a nervous breakdown if your Math dips to 660 and your Writing to 630. Yes, it’s nice to maintain, and yes if you do get your CR score up, you will have to send that score and have colleges see that you went down a little in the other sections, but as long as the drop isn’t truly alarming (e.g 150+ points), it will not affect your chances.
College admissions officers are human — they know what constitutes a normal range, and they know that variations in mood, location, amount of sleep, etc. can produce variations in scores. They know that the difference between an 800 and a 700 in Math and Writing can be as little as four questions. If you go down a little, they’ll take the higher score and won’t hold the lower one against you. Really. Even if you got an 800 the first time and a 740 the second.
The other reason they’ll only use the higher score is that college rankings are determined by admitted students’ SAT scores, and they want their school’s scores to be as high as possible. It’s in their interest to do so.
So the bottom line is, don’t sweat it. Go in, do the best you can, but focus a little more on the section(s) you need to pull up. If you’ve got that score down, don’t deliberately ignore it (schools will not look kindly on your blowing it for the sake of blowing it), but don’t stress excessively about it either. You’ve got other things to worry about.