Hi Anne, that's certainly far better than my first attempt at a pano. The reason your pictures are soft is that diffraction starts to add significant blur after f16 (in fact, it can already be quite bad by then).
You locked the focus (good). Did you lock the exposure as well? If you let it automatically recalculate the exposure for each frame, then you can end up with banding problems. I can't see that here though (it's just you mention 2 shutter speeds but didn't mention manual exposure).