Hi Andrew and welcome to the group. Nice work on restoring the Bengall so far. I think it likes you cause it gave you a little love bite.
You have to take care sanding around the edge, and as you found out each change in grit adds a little something to the edge.
Have a look on the restoring threads for a sanding jig. They are simple enough to make and can save some nasty cuts.
I look forward to seeing the finished product.