I think one thing that helped when I cut my shoulder length hair off was that, hey, if I was unhappy with it, it could always grow back out. For the most part, hair is a pretty adaptable thing and can grow back out. I actually ended up liking the change, to be honest! It felt different to not have so much hair, but in a good way. There was less to care for, after all! And while I sometimes miss my long hair, I remember that if I ever want it back, all I have to do it stop trimming my hair. :p
Dig around for a good person to cut your hair off, someone that will LISTEN to what you want. I had a friend who just graduated from cosmetology school cut mine, and we had fun. I only spent like $10 USD on it, and we ended up hanging out after and I got a lot of compliments from people. Granted, I'm out to most folks, but still. Short hair isn't always seen as a bad thing on "girls". Look at actress Emma Watson, she looks pretty spiffy with short hair and while you always get people who complain, a lot of people think she looks good.
Anyway, it's your hair! Only cut it if you want to, okay? It's okay to be nervous, change is pretty weird after all. But not all change is bad change in the end!