Clothing change assistance

I'm signed up for a sprint triathlon in 2 weeks. I'm doing it as a friend and for a once in a lifetime experience with the goal of finishing. I will be 10weeks pregnant at the time of the race (found out after I paid for it). I don't have much money so new items are out of the question. I NEED to be comfortable. I'm not a strong swimmer and borrowing a wetsuit. I own one one piece bathing suit completely unsuitable for running. I need to take off my suit and put on clothes. All the tips I've seen either say to buy a tri suit or wear a 2 piece bathing suit and complete the race in it. I can't do either of these. Please, is there anyone out there that has changed their clothes??? I realize I'm out of my league here, but either I formulate a game plan for changing somehow or I don't go. I tried today and couldn't do it without flashing an audience from underneath my towel. Maybe a big t-shirt would help? Wearing my sports bra and thong underwear under my suit, trying to keep them on when I take off the wetsuit and suit, and then putting my capris and tank over them? Is there a port o potty that I should run to and change in? Please help. There has to be someone else that has experienced this!