On an SAT Subject Test, I scored a 790, 10 points away from a perfect score. The issue is, despite being so close to perfect, I only scored a 75 percentile.

An 800 would've only allowed me to get a 79 percentile according to an online table.

Are these percentiles based on Scale Score alone or the number of questions got wrong?

If I am trying to apply for prestigious colleges like Ivy League universities, will this score overall help or hurt me if I am planning to major in the subject that I took for this test? Will they think less of me because my percentile is so lower or will they actually like this score?

I won't be able to retake this SAT Subject Test due to a tight schedule, so I would appreciate some tips and thoughts concerning how such colleges would judge this subject test and how the percentile is determined.

Honestly, it depends on what they ask from you. Did you email them to see what is their min score they want? If not do so.
If they answer you and you see that your score is below, the only way to do it is re-do your test.
For example, I asked my university long ago what they want the SAT scores to be and after I did my test I was missing 23 points. So now I have to re-do it if I really wanna go there.
Hope this helped :)

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