Firstly, if you're nervous on him, get a few lessons on her. There are no words to the value of a professional telling you and showing you the correct way to do things.
If you don't want to take lessons, there's a few things you can try.... I don't know your skill level (I'm guessing beginner, I appologize if I'm wrong) so I'll give you just a very basic idea to try. The big thing that would help you immensely is a soft mouth and that she gives to the bit. When you put pressure on her mouth, she should give to it. If she's pulling against you, that should be your first mission. From there, it can be just a give and take. Hold her for a few seconds until she slows down a notch, then release. She'll speed back up, but it takes time. Lots of repetition. Don't worry too much about stopping, backing up, and repeating until you have a bit more control over the lope. That will help more when you're looking for consistancy and needing her just a little slower. Depending on your horses temperment, that could get her hot and bothered. If she's lazy, though, it could help.
I won't discribe more technical things to try because it probably won't make much sense. Things that like need to be shown, not read. I think a few lessons are your best option though.
Definitely take jumperwithfire's advice getting relaxed and comfortable. It will help you immensely.