I guess it's difficult to provide an absolute solution without seeing what he's doing. Could you post a vid of how he's jumping? Might help with the exercises...
One thing I did notice about Clippy is that he seems to be developing a lot of muscle on the underside of his neck - this can be due to a high head set and 'bracing' against hands. As my instructure says, when you get to that position, the ball really is in the horses court! :)
If this is the case, the I'm afraid it's lots of flat work. MIEventer and Spyder have written many articles on what the correct frame should look and feel like, and useful exercises to achieve it (Much better explained than I could ever do!) With the 'energy' coming from behind and the horse forward and soft into the contact, you're then in the driving seat! If a horse is carrying itself (and you) correctly, then it makes it very difficult for the spooks and bolts to occur!
Ok - so we now have the correct frame.
Next step is to ensure the canter is 'organised'... (note all this is done without jumps!)... By organised, I mean it should be rythmical and a steady tempo (count the beats in your head or canter to music). The reason why I feel this is important, is that I think a lot of horses 'rush' to compensate for being uncomfortable/disorganised/over-faced. Again there are a lot of flat work exercises for this... circles, transitions, spirals, extensions...
Then move onto a course of canter poles... aim to maintain the tempo even when riding the poles!
Finally - and could be done in conjunction with the canter work, introduce grids and cavaletti work. Note that even by this point the aim is not how high, it's maintaining that rhythm! Start simple like trotting cavalettis, with an element at the end.... and build up to more complex patterns like jump...stride...stride...bounce.....bounce etc. It's great for improving bascule, agility and providing a mental work-out to boot!
My pony I rode when I was about 15 used to charge jumps. I had a really great instructer who helped me through (similarly to what was described above). We didn't jump anything over about 50 cms until we'd developed the correct paces and 'shapes' over fences... It took us nearly a year to perfect! Then one day she put up a 1m, and we just 'popped' right over... in fact it didn't even feel that big!
Please make sure this is sorted before you try the x-country you want to do! Because we want you to be safe!!
As for not liking dressage... why don't you mix it up by having a friend/sister shout out commands (like trot to canter... 20m circle at A... shoulder in... etc) to make it a bit more of a challenge and more varied??