I think only your doctor can explain precisely what s/he means by "pelvic rest and take it easy." I'm kind of surprised s/he didn't spell that out for your clearly when you were seen. When I was put on rest, I was told exactly what I was allowed to do and for how long, how frequently I had to rest or lie down and again for how long. Unless you are local to WDW, the last place you really want to be with complications is away from home and your own doctor. I honestly wouldn't travel. It's disappointing, but call WDW and see if they will work with you to reschedule so you don't have to outright cancel. Of course, each doctor's interpretation of "rest" can be different, so please discuss your trip with your own medical provider.
Good luck to you and your little one!