AAMC limits you to 3 attempts within a single testing year, 4 attempts across any two consecutive years, and 7 attempts total in a lifetime. Every school you apply to sees every score from every attempt, not just your highest one, so there's no way to quietly discard a bad sitting.
One retake that shows a clear, meaningful improvement is completely normal and rarely held against you. Three or more attempts start to genuinely worry admissions committees, regardless of the final score. Retake only when your recent practice test scores actually show the improvement you're hoping the real exam will show — working with a tutor between attempts is often what turns a second sitting into a real jump instead of a repeat of the first.