1. If my memory is correct it is prohibited to slip a C-172 at full flap.
2. It is prohibited to slip an older C-150 (with 40° flap).
That being said, you want to loose heigt FAST?
Get as far away from best glide speed as possible.
Options:
a) GO full flap ASAP, and DIVE at max flap speed, aim about 2OO yard in front of the touch down point, to get as much resistance as possible, then flare just above ground. A full flap C-172 is draggy.
b) GO full flap ASAP, and slow down to just above stall speed streight ahead, DO NOT BANK or you WILL STALL/SPIN in, and let the airplane sink. The lower speed will cover less ground while sinking fast. At 50ft a gentle forward nudge to get some speed to flare properly.)
c) GO FULL rudder slip without flaps, at well above stall speed. (the higher the speed, the more drag you create.) Aim 300 yard in front of touch down point
But then it gets complicated. Level out, drop full flap, flare, a lot to do in little time, and judgement will jhave to be perfect.
These are things to try out at altitude like 3000-4000 ft or so.