You know, when my students come to me with similar issues, I do a few things. First, I treat it the same as if I was training a horse, and that horse needed confidence over fences. I'd do the smaller stuff til the horse was bored, and wanted to do more, and then I'd raise the fences. From time to time I'll also bury a bigger jump in the middle of a combo/grid where it's got a nice easy flow to it, and the horse (and rider) won't notice as much.
From there, I'll also make a point to keep the student talking to me about how they are doing and what they are feeling between fences and take their mind off the jump itself (not on approach! After jumping around the ring!). I've been known to raise the fence a hole or two when the student isn't facing, in a non-obvious way, and then after they've jumped it, said oh hey, did you realize that I raised the fence and it's higher? That ONLY works with the right student though. Some of my students I would freak out if I did that. Others don't even notice and are nervous, but as long as I tell them it's not that high, they are like oh okay cool! So take that advice with a grain of salt and don't push yourself if you're not ready.
Often I'll say yeah that's 2'6". And they will say are you sure? I say yup, same height we've been doing. The rail is just skinner/fatter/different color etc. and that's why it looks different. Then when they are done I'll go nope it was 2'9" and check that out you just jumped it in both directions 3x each with ease ;)
Most importantly, be patient with yourself and know that repetition pays off best imo. Pushing yourself too hard too fast can result in a loss of confidence that takes ages to rebuild. Far better to be bored for a few weeks than to spend months rebuilding b/c you were overfaced and scared - and it doesn't take a fall to feel that way. Sometimes you CAN make it over the fence and still have your confidence shaken. Trust your gut (and your instructor assuming you work well together) and above all, BREATHE! Good luck!