Should I submit a Standardized test if it’s optional and I’m just below average?

Answered

With the way test optional schools have worked in the past, there's always been an inherent advantage to submitting scores as long as they're around or above the average for the school you're applying to, and a disadvantage to not submitting them unless your other factors—GPA, coursework—are well above average. So what is the rest of your application like? If your GPA is extremely strong and you've taken a ton of AP classes, you'd probably be fine going the test optional route, as a 31 isn't going to move the needle much in either direction. But if your GPA, coursework, etc. isn't the strongest, I'd still submit the score.

Incidentally, when looking at averages for test scores, GPA, etc. for schools with holistic admissions, you also need to take into account what students you're going to be compared with. E.g., if you're from an over-represented minority background, the "average" score they compare you to will be higher than what you see on PrepScholar or CollegeSimply. If you're from a URM background, then it will be lower (in this case you'd be absolutely fine submitting a 31). I'm pretty sure CV's chancing engine takes that into account, so I would also go through the chancing profile on here and see what your list looks like with that score vs. without it, or with a score one point higher (so you can see what the difference between a 31 and 32 is). That might give you a more data-driven indication.