Windy, I would carefully weed out the Morning Glory in the area where you planted your Maypop seeds on the off chance that there might actually be a Maypop vine struggling along under the Morning Glory. MG twines around other plants and virtually smothers them, but Maypop is pretty vigorous. Watch for thicker straight (not twisting) stems and darker green, lobed leaves.
After that, my current favorite blanket weeding method is clear plastic. (only if there's nothing else under the MG's that you don't want to kill) Cover for a few days with painter's drop sheets and let the sun do the work. You will still have to clear them out but it's easier once they're dead.
BTw, do you remember what the seeds looked like that you thought were Maypop? Morning Glory seeds are about 1/4in. long, narrow, sort of triangular with one pointed end, and the Maypop seeds would have been flattish and rounded.