Thank you both for the replies! I went to the Dr. today and everything is fine with both of the babies : ) one heart rate is 131 and the other is 121 so they are happy with that. I know I still have a couple hurdles to get through but at least that's one less worry!
I honestly wouldnt worry about it at all. My twins have been a week apart from the get go and I am now 25 weeks along. And guess what, they are STILL a week apart. What the doctor told me is that it looks like one implanted on a different date than the other and that there was nothing to worry about. Most of the time with (fraternal) twins they will be different in size as all babies are different. Good luck to you and please keep us updated.
A friend of mine at works wife had the same thing happen to her. It just happens sometimes. Guess all you can do is be happy about the one. BU you never know, the other one MAY survive.