My doc, who had last completed Danskin 9 years in a row, said that her first time, she doggy-paddled all the way through a 1/2 mile swim and said she was absolutely positive that she did not even get her eyelashes wet. Go for it! It'll be fun. And then eat your cake. :-)
"My predominant feeling is one of gratitude. I have loved and been loved;I have been given much and I have given something in return...Above all, I have been a sentient being, a thinking animal, on this beautiful planet, and that in itself has been an enormous privilege and an adventure." O. Sacks