When is my period going to start also how to make my period start before I go to a dance!,!!!!!!!!!!

I'm 12 almost 13 and I've not got my period but I have this gooey discharge! how do I know when my period is going to start because I have a school dance in 4 days and I don't want to be wearing a dress with no pad and it starts! also how do I get my period to start!