Your SI is the sum of your 3 test scores (Reading, Writing and Language, and Math) multiplied by 2. It should be 224, based on your scores.
However, if your school offers a January PSAT/NMSQT, the NMSC may not accept the SAT in lieu of the PSAT. Since you got a 1510 on your SAT, AND the SAT is a bit more difficult than the PSAT, AND you are more prepared for the PSAT than you were for the SAT, you likely do not have to worry.
If your school cancels the January test, you’re good. If it doesn’t, you’ll likely need to take the PSAT in order to qualify for National Merit.
So. plan to take it, in the knowledge that you will likely do very well on it, and there is a very good chance that you will be a semifinalist. If you do get higher than your state’s cutoff, your SAT will provide your confirming score, and you will also be halfway to Finalist.
Check out Art Sawyer’s article “The PSAT and National Merit for the Class of 2022” at Compass (compassprep dot com).
Good luck whatever happens!