Bridesmaid Period drama -- Help?

Well, I am 15, and I started my periods around December 08. My last one was in late April, and I understand that they will not be regular straight away. The thing is, I am going to be a bridesmaid in mid-august. I feel really un-girly and gross at during "that time" and the last thing I want to be doing is wearing a short, lilac dress, having pictures taken, smiling, dancing, and running to the toilet all day. I was really looking forward to it, but now with it just a month away, I have realised it could possibly ruin it for me. What protection do you suggest I use? I prefer not to use tampons, as Ive never used them before, and Im still very new to periods, but what else do you think I should do?