New steering coupler doesn't fit!

turn the steering gear to where the master spline in shaft is top center. Position coupling same ( notch at lower outer edge is reference ). If the coupling starts on part ways you have that much correct. There are voids in the splines where the cross pin goes so the coupling can easily get misaligned and hang up there. To simply begin hammering can create burs and do more harm than good. The marking used before are still there to see. Shake, wiggle, downward pressure, light pecking with hammer to start it on its way again. You may need to use a small file to remove some burs on the shaft and inside the coupling.
If the steering gear could withstand a lot of abuse at its input shaft, the coupling wouldn't have been needed. If it was in a place where one could get serious hammer blows to it...