My score dropped by 100 points?

I’m not worried about the composite score drop. What worries me so much is that I’ve dropped by 110 points in math alone for some reason. I went from 800 to 690 and I don’t understand why or how. I’m really nervous because I want math-related majors. Let’s suppose my university does not superscore. How would I look like to them… with an 800 in Dec that’s suddenly a 690 in January, the lowest math score I have ever gotten on any trial, and I never got such a score on any practice test… (my lowest on real SATs was 720 (-2), and my lowest on practice tests was 760 (-2) )

I hope somebody will help you find out!