Drive to Aviation House at Gatwick, put your licence on the CAA's desk and back slowly away without sobbing, like any man would.
Seriously, if you weren't reported you will possibly hear no more about it. Theoretically you are obliged to inform the CAA that you breached the ANO (but I'm not sure that anyone has ever done so for such an incident).
If I were you, I'd put it down to experience and vow to plan more carefully in future, which I'm sure you will.
Or buy a radar altimeter.
Take care.
