Maybe just stick the the height you're comfortable with for now until you almost get bored of the height and it becomes too easy, they slowly move the jumps up one hole and keep going until you feel confident and it doesn't scare you. Just take your time and eventually you will trust your horse answer he will trust you and you will be able to jump him over almost anything you want
jumping rows of bounces where you gradually raise the last one helps to build confidence, because you see what happens over bigger jumps (nothing other than over 2'9 ;-)...) and don't have to worry about distances
Try to take deep breaths and just slow down your heart rate so it would be easier to stay calm, focus on good rhythm at the turn and always keep your contact and don't rush to the distance, just wait and sit. Also you can try putting ground poles before the fence maybe like three because to some people it might be difficult to find a distance to a pole before a fence but with three poles (one stride between each) it's doesn't cause brutal situations if the distance isn't perfect. Also with poles the bigger jump just "comes" to you. Bigger fences can also be trained with combinations, regular or triple, by putting the last jump higher. Just by jumping bigger you become more confident to jump higher, after every bigger jump you get more used to them and it becomes easier every time! :) But don't push yourself to fast or hard and try to jump bigger with a confident jumper!