I once had an instructor who would put up the jumps higher without warning, and she would push me to do all kinds of scary jumps that I wasn't ready for. I mean, I was physically ready, because I did jump up to 2'9'' with that instructor, but I was not mentally ready in any way. Eventually it got to the point where getting over the jumps was more of a relief than it was fun.
Now I ride at a place where the instructor has only been setting the jumps up to about 2'3'' - 2'6''. To be honest, I'd rather jump up to 2'6'' and have fun than be rushed into jumping any higher.
I'm not saying you won't have fun jumping higher. But think of it this way (this is how I think of it, so it might help):
The height of the jumps does not determine how good of a rider you are. And just because you are not jumping progressively higher in your lessons does not mean you aren't advancing. There are so many more ways to advance besides jumping higher. In my lessons, the height stays the same, but we learn to do things like courses and grids. The jumps are set up differently each lesson and it is always challenging and exciting.
A person who can jump a 3' vertical in the center of the ring may not be able to get around a full course of 2'6'' jumps, and vice versa. Both riders are advancing, but if you have a jumping limit, you will just have to keep learning and improving in other parts of your riding, by challenging yourself and working on bad habits, etc.
Hope this helped!
Every ride, good or bad, teaches you something new.