Ah, reminds me of me as well a few years back. There were many times when I was under par with a few holes left. I started thinking too much of "what could have been score" only to see my score go back to even or over par. I finally did eventually manage to break the under par barrier and here are some of the tips that helped me overcome that:
- Stick to your game plan, and most important of all
- Think execution and not results when doing your shot

My goal now is to score in the 60's. My best score is 2under par but that was with birdie on the last hole so have never been in contention of doing it.....