Having issues with daily myoclonic jerks and balance issues, b12 is 277 (neurologist said it's considered slightly low even though it's within the range and she'd like it to be 400) but mma levels came back lower than average. what does that mean?

Lower than average MMA level may indicate that you do not have B12 deficiency since MMA builds up due to inadequate vitamin B12 levels, it is used as a functional indicator of vitamin B12 status.

Hard to implicate B12 as culprit at this time due to MMA results, but do boost levels, nonetheless. The etiology of the myoclonus needs to be pinned down, and at least two, of the standard medications used in epilepsy, should control this. Work closely with your neurologist, and get stabilized.