Why is no one teaching you about visual aiming points/reference points ?
If you are getting it right the reference point remains constant on the canopy relative to the horizon, if you are undershooting your chosen reference point goes up the canopy and if you are overshooting your reference point disappears under the nose, you can compensate accordingly with power or attitude adjustments - once you are over the numbers dump the power and glide it down (using the old Mk1 eyeball to judge the distance/angles).
It's real basic, shortstripper is right. 1 hour in a motorglider with about 15 circuits/landings will soon sort you out !!
I've never used a PAPI in my life - surprised a low time pilot even knows what they are !!! (only just found out what one is myself !!!)
and good luck !!
Arc