Nothing like waiting til the last minute to ask for help...!
Generally, the best thing to if you are trying to fade, is keep them at bay. There are kind ways to tell them, "Thanks, but no thanks. Not at this time. Thank you for your interest. I have your number and will phone you if I feel I need assistance [from you]."
But since you have already committed, my best suggestion is to leave them a phone message stating that something has come up and you are unavailable to meet. Then go treat yourself to dinner and a movie in a town where they don't live. Come home after 10pm pour yourself a little glass of wine or cup of tea and go to bed.
It's a much better use of your time.
Good luck. I wish you the best.
-Aude.