How can I regain her trust?

My girl and I broke up a few months ago and recently got back together. While we were seperated, I made plans to meet up with a girl I used to sleep with who lives in a different state. Well before I was supposed to meet up with this girl, my current GF and I started talking again so I cancelled my trip. But I told her that the trip was planned with a friend of mine, not that I was supposed to be meeting up with a girl. Well of course she found out the truth and is very upset that I lied to her. I explained that I planned the trip while we were apart and didn't want to upset her with the real reason which is why I lied. But she is convinced that she cannot trust me now. She has also found out that I had lied about a few other small things while we were together which makes her trust me even less. I have never cheated and would never cheat but since these little lies I made have come up (and I have come clean about all of them) she says she can't believe anything I say. We have made an appointment with a counselor (my idea) to help us through this but is there anything else I can do to regain her trust. And yes, I know that not lying anymore is where I need to start which I have.