My kid was TO and got into all her applied boarding schools. I didn’t think SSAT would help her and she had other strong parts of her application and of items showing boarding school readiness. However she did not apply to very academic boarding schools, but more middle tier Mercersburg, etc. She chose Emma Willard in the end.
As a freshman her grades reflect the strengths and weaknesses she has always had. SSAT did not reflect on how she’d do. Subjects where she had been very strong are still very strong, even though SSAT score was poor. She’s been assertive in seeking out help as needed. The school seems to be a very good fit for her in many other ways.
So the SSAT is just one number that gives some guidance to you and the school, but you could have other data that gives a different picture.
I’d probably apply with that score especially if you show math strength through other means.