Help pls

I'm going to a lake with my friends on the last day of school which happens to be my suggested first day of my period. The app is almost never right (I'm always a couple days early or late) and I don't want to shove a tampon up there dry and have to pull it out dry but I can't wear a pad on a swimsuit and I don't want to bleed everywhere. I can bring a tampon but I normally wear pads so sticking in a tampon is uncomfortable. I also may wear the swimsuit to school which would make it more complicated ugh. Pls leave suggestions to help a sis out 🙄