Hi,
Welcome to the Honda forum.
It could be that your shift shaft is out of adjustment. You can adjust it by finding the long barrel nut at the front of the lower extension case where the shift shaft exits the front of the gear case.
You need to shift the outboard into REVERSE while slowly rotating the propeller to check/adjust the shift shaft.
See items 11, 15 and 39 in the link below.
What often happens is that the jam nut (item 39) comes loose or isn't tightened properly and allows the long barrel nut (item 11) to rotate and change the adjustment.
But, if you find that the jam nut is tight, the shift shaft might still need an adjustment.
You will need 2 good quality, open end, 10mm wrenches to adjust.
To adjust, back the jam nut away from the barrel nut.
Turn the barrel nut UP the threads of the upper rod until it releases the lower rod.
Reconnect the barrel nut to the lower rod and turn it downward 8mm. Lightly tighten the jam nut and check how the outboard shifts.
Always slowly turn the propeller while shifting when the engine is not running. It does not matter which direction you turn it just so long as it is slowly rotating. You might need a helper to do this.
If the outboard shifts from reverse to neutral to forward then back again easily, fully tighten the jam nut while holding the barrel nut stationary.
If the shifting isn't smooth, you may need to readjust slightly.
When you get the shifting to happen as smooth as possible by making very small changes, fully tighten the jam nut while holding the barrel nut.
You will then need to test it with the engine running in water.
I hope this helps.
Good luck.
