I agree with Kate it's not a big deal and I had that same problem. My mom wasn't there when I started only my dad an my sisters were. I told my older sister and we were both like 'how can you get your period so young?!' but hey it happens. And looking back I was only 11 but its a lot to go through at 11 when you moms not there to talk to. I had to wait 2 days to tell my mom that I got my period. I just kind of said it bluntly 'mom I got my Period' it actually isn't as akward as it seems. Also my sister was always by my side even when I told my mom. So if you have a sister or maybe a really close friend that could be with you? I found that that helped out a LOT!
Good luck
Brittany X