Yes absolutely. Percentiles are often talked about as the percent of people taking the test that you scored better than. (I'm no statistician, and I don't think this is the exact statistical definition, but it's close enough.) So, if you scored in the 50th percentile, you scored higher than about 50% of the field.
That relates to the common confusion of the "100th percentile," which technically doesn't exist. Simply put, this is true because you can't score better than 100% of people taking the exam - it's impossible because you can never out-score yourself.
In relation to the MCAT, though, I see what you're asking. There can never be a concrete, predictable correlation between the number of questions that you answer correctly and your percentile, because the difficulty of each MCAT isn't identical. (Imagine if, by some ridiculous chance, half of the test-takers on a particular day missed every single question. If you then got one question right, you'd fall at the 50th percentile.) But the AAMC makes sure that scaled scores correlate pretty consistently to percentiles. If you're aiming for the 55th percentile, your goal is definitely in the 501-503 range.
Good luck 🙂