I wasn't waitlisted, so sorry if I'm not much help, but I think you may have a good chance. The admissions at MCPHS are very nice. Probably the nicest people I've ever met. So if you stay in touch and show your interest, I think it would help you out a lot. Also, a lot of people choosing other schools would most likely have to put in a deposit by April, while MCPHS continues to accept students till May, I think. So this would open room for the waitlisted folks since a lot of the students that may have had MCPHS on hold by getting accepted to MCPHS would be released if they chose another school. But definitely submitting your new scores as soon as possible would increase your chances because it does depend on the number of seats.
I just respectively declined my offer at MCPHS as I got into another school that was of more convenience for me, so there's one spot already! Good luck!