I was wondering if you had any advice or exercises to help my sit ups?

The most easily correctable things I see guys do is 1) hips are too close to your heels and 2) doing negatives on the way down. That will give you a few more but overall I would recommend just varying your training if you can when you are doing ab exercises. Look up some ab exercises you have never done and just do a 10 min session of whatever that exercise is and you will see a difference.