> Everytime we've been looking at some particles we deemed fundamental they appear to be made of even smaller ones.

Not everytime. There is a list of particles that we currently deem fundamental, because no one has found any structure in them. But maybe we haven't looked closely enough yet. Some entertain the idea that they consist of vibrating strings instead of structurless, pointlike particles, but then those would be fundamental.

Well, electrons are sort-of fundamental.

But they can also be seen as quantized excitations of some underlying quantum field.