First of all, you shouldnt be ashamed of what happened to you. Its not your fault that you were raped at 13, so dont let ANYone try and make you feel like you need to hide that or explain it. It is NOT your fault, ok?
Secondly, I agree with Josh, you probably should have been honest in the first place but I'm guessing you already know that...and theres no point in dwelling over 'if only's...its done now, so you just have to try and put things right.
I dont know how long it is until your 14th birthday, but, seeing as you are still 13, you have still lied to him by telling you are 14, right?
I can understand why because 13 does sound very young and its easy to imagine someones reaction...but its hardly something you want to base a relationship on.
Anyway, there isnt much point in me telling you what i would do in you position or in his, because its not about me, its about you...and him.
It might be an idea jsut to have a think about what you really want from this whole relationship. I mean, where do you see it going, what are you both getting from it? I obvioulsy dont know either of you but in my experience, an 18 year old wants very different things than a 13/14 year old in a relationship...
But he said you could call him, right? Which suggests he wants to hear from you, but you need to think about what you are really wanting...I dont know if you would rather talk to him, explain to him how youre feeling...have you thought about being just friends? Maybe thats something else you could talk about.
If youre serious about this, I think youre going to have to be a bit more honest with him. Its difficult, because you arent right there beside him so he cant see your face, he cant see your expressions, he cant hug you to make everything right, you need to talk to him about it, tell him exactly what you want him to know, because that is the only way he can find out.
Well, goodluck with everything! and eek! sorry for the long post!