Cutting underfloor heating cable

Difficult to comment without knowing what you bought.

I suspect you can't cut it as you'll change its resistance and power rating (and may have problems making connections to the cut ends, not to mention that it might also be screened as a leakage protection).

You'll have to change the spacing to fit it all in.

Do not, under any circumstances, shorten a heating cable. This would reduce the circuit resistance and thus increase the heat dissipated per unit length. (Double whammy - more watts in fewer metres.) The cable would be over-run and the power per unit floor area would be higher than if you just fitted it all in by slightly reducing the spacing.

Manufacturers' repair kits are available for where accidental damage occurs, but as I said, *DO NOT CUT*!

This sounds like nonsense. If you only have a small amount of 'excess' a small reduction in spacing will easily absorb it and the increase in watts per sq. m. of floor area over your design value will probably be negligible.

forget cutting it. Space it closer, and if you're keen to reduce power per area use a dropper or transformer