Have you thought about buying used?
There are some immaculate 2019
Cupra Lux on Auto Trader for 25k and under, and you could be in one next week. Or as others have suggested, buy from stock? Not sure what colour you originally ordered, but if it wasn't grey then you'd be accepting a different colour and different model, you might regret that down the line - although it does look lovely in grey.
In the current climate I wouldn't wait for your lux to be built - too much uncertainty with the virus and incoming mk4. I also wouldn't expect there to be much price difference - the only reason I ended up with the Lux is because it was only £4 extra per month.