Keep in mind that the Top schools are ranked as such due to their emphasis on research and the high amount of research funding they receive. Two-plus years of a substantive research experience would make your chances better, along with strong leadership if you're aiming for the most selective schools.
Also, if you rank schools by selectivity, it isn't until you look at the ~29th school that the median MCAT score is below a 34.
It's my understanding that withdrawing from your early assurance med school will not count as a mark against you, but keep in mind that folks with great stats don't always get an acceptance, possibly due to red flags in LORs, poorly written Personal Statement, insufficient ECs for a given school, or shakey interview skills.
Also, a 33 on practice tests does't necessarily equate to a 33 on the real thing, so you might wait until you get the score report back before withdrawing.