Even though you are a male, you might want to go get a pedicure... the technician can cut and shape your toenails so that they look great in sandals. She/he can also clean out the dead/extra skin around the nails and on your heals, but you can skip the polish.

The Lamisil will continue to work, don't worry about that.
Go to Cancun and have a great time. You will be worrying more about your nails than anyone else you are with.... they won't even notice or look at your feet!