Remember the cause of the bumps. It's air that is rising or sinking in a column.
Of if lower down, such as in the circuit, you may be getting "disturbed air" as it flows over the local terrain (building and trees for example).
When you do a cross country (not sure if you've started any yet), watch out for different surfaces. You'll often notice a bump when flying from land to lake, or over a town etc. Here in Ireland we have lots of bogs. As you start to fly over them, on a summers day, you are virtually guaranteed a bump, and another one as you leave it again. Try to predict them. They won't bother you as much if you're expecting it to happen as you flew over a different surface.
If you don't predict it, at least have a look below/behind (or if low down, look upwind) and try to figure out what caused it. Understanding something is be best way to overcome a fear of it.
dp