My first period ? Concerns ?

Im 13 and started my periods at school today. i had no protection with me, so i borrowed off a friend. i was really scared because im not very good with blood and alll that gory stuff . i was really concious for the rest of the day that it might come throo and onto my skirt. how can i not be so worried ? My mum knows, but she just sed you usual soppy mummy stuff .. like aw u growing up. my ickle baby. all tht. but im actually really scared bout being on at school. ??