say you just got into a fight with your girlfriend and she sent you a email saying:

I want you to know that I am sorry that I caused us to end what we had. I said some hurtful things and got angry at you for the wrong reason, and really I was the one to be upset at. You are a great person and I would hate to lose you. I know this may be hard for you but I would really like it if you would at least forgive me and at least try to give me another chance.. If you aren't ready for this I will try to understand. Please let me make it up to you.

he hasnt responded yet but I dont know what he will say im kinda scared

When did you send this? Are you sure he's read it yet?

He can say one of three things basically, yes, no or we'll talk it over... if and when he decides to get back to you. Don't nag and don't panic. If he can't appreciate that you try to work things out in an argument and he can't get past that then he isn't worth it.
You did the mature thing to own up to being in the wrong, now the ball is in his court.

Without knowing the details of what the fight was about or what the specifics are, your email sounds rational and reasonable. There are obviously a lot of things that could influence what sort of response you'll get, like how long you've been together, how old you are, etc.

In general though, your message is rational and not too clingy. I know it can be tough to not let your mind race and be thinking about it all the time, but if you start following up with more email or phone calls, you'll come across as desperate or needy, which it doesn't seem you are.

I think your best bet at this point is to try and relax and wait it out.