OK - Back to basics.
You need to see the 'shape' of the runway environment in order that you might start to remember the correct aspect. Ask for your instructor to demo this - at your stage I'd suggest that as much as 1/3 of your time in the circuit should be in the form of (immaculately flown), well pattered demos.
I'd also ask for the PAPIs to be switched off.
You instructor should also demo being above the glide slope and below the glide slope (not the instrument slope necessarily!) and teach you both how to recognise and how to correct these situations.
Constant or fixed aspect priciples work well as something to hang your hat on - if your desired touchdown point is not moving in your windshield you will hit (land!) it. If it's moving up you are going low (undershooting) if it is moving down you are going high (overshooting)
At the touch down point - can I suggest some golden rules:
A good landing rarely follows a bad approach
Three main sections of the touchdown phase are quite clearly defined as; Flare - to stop the rate of descent; Fly level a foot or two above the runway as the speed decays; Settle onto the mainwheels. Note - It is not possible to go from step one to step three missing step two!!!
Finally, once you have mastered Biggin get your instructor to take you to other runways (shorter, narrow, wider etc) so that you can get the feel of how runway shape can affect your perception of vertical positioning on the final approach.
Have fun...