Running half marathon on Saturday and just got my period?????? PLEASE help!!!?

Hey guys! :) I am 15 and in two days am running a half marathon. The WORST possible scenario is for me to get my period, and today I started seeing little drops of blood in my panties :( The last time I had my period, it was SO heavy that I was bleeding through like 7 maxi pads a day, and I was throwing up and everything (fevering, etc). It was probably the worst, most painful 11 days of my life (AND my periods last forEVER!) If this is what is going to happen for the next couple days, there is NO way I will be able to run this half marathon! I have already paid 50 dollars for everything, and have been so excited, and I am going to cry if I am miserable because of my stupid old period that day!! Plus, if I DO have my period, what am I going to do on race day?? I tried my first tampon last period, and I am still not comfortable with them at all, so that's not really an option, and then wearing a HUGE maxi pad for four hours (while running and sweating and everything) does NOT sound too fun at ALL! I REALLY need some help out there, girls! Thank you SOOO much! :) Any suggestions or tips would be GREATLY appreciated! :)