Why does this have to happen?? its so stressful!!! :(?

I just got my first period yesterday..(tuesday) and i was supposed to have a pool party on thursday..but i had to move it to the next week so its going to be on thursday the 30th...so do u thnk it will be gone if it happened on the 21st and the party is on the 30th?? HELP!!! and in school...idk how to deal with it..how do i?? and i am also scared to use a tampon...HELP!!! :(