That sucks, falling into a jump is never fun and often painful.
Try a double cross rail with the backside one slightly higher than the front, and keep them as close together as the standards allow. Then progress to a cross rail with a vertical as the over, but no higher than the outer side of the cross rail. Do this until you are comfortable then make a small oxer, with the front one 1 foot and the back 18” or so so it’s ramped and easy for you to judge.
When jumping the oxer, you should be looking at the back rail, not the front one.
I had a fear of oxers until recently. I’d suggest starting with smaller oxers, such as ones at cross rail and low vertical heights and just practice those untilyou feel comfortable. Then gradually raise the height and width of the jumps, getting comfortable over each size. Don’t push yourself too hard that you completely lose confidence over them but push yourself a little bit so you are able to work through it. I hope this is helpful and good luck!
Hi Maeve, perhaps start small, narrow, and square, even to the point of it looking like a vertical. Keep riding to where you feel comfortable, moving higher and wider slowly as you start to feel more confident. Instead of focusing on the jump, keep bringing your mind to the job at hand, especially when approaching. Wishing you all the best in overcoming this fear! It can be quite tough, but you are making progress just by the fact you are searching for a solution!