Potential period problem, what should i do?

so i THINK i got my period for the first time today like it was browny/red today (but not too much) this afternoon and none tonight so idk if its just like spotting like if its gonna come in awhile, or if i actually have it already. Anyways, my problem is, my friend is having a pool party tommorrow and i know i could just wear a tampon but if i dont have my period i shouldn't wear one.. and that would be SO embarring and unsanitary if i got it in the pool, so awkward! so what should I do? I cannot miss this...