You were lucky that day when you tightened down the compound. I find that having a selection of MT sockets or adaptors helps a great deal used as test pieces. It is possible to detect which end of the taper is loose when the socket is held lightly in the fingers. As the fit gets close, a little engineers blue will enable a perfect fit. Of course, getting the angle perfect will be hit and miss. I use a proper taper turning attachment on the Smart & Brown model A, but this although able to be much more easily finely adjusted than any compound, it is still much too coarse to get Morse tapers without trial and error. It is important to get the tip of the tool exactly on the centreline with any taper. Unfortunately every different size of Morse taper is a different angle.

You might try polishing the taper you cut with some emery paper and oil to get a smooth finish, then check your reading. If it is still good, you could drill and ream a dowel hole through the topslide and cross slide for future use with no set up time needed. Just drop the dowel pin in and go.