I’m in the uk too. I just looked up a converter online and wrote it onto the recipe myself. Something like this
https://www.thecalculatorsite.com/cooking/cooking-calculator.php. A cup is a measurement not a coffee cup. A USA cup is 240ml (an Australian on is 250ml btw). A lot of recipes for low carb and keto are USA based and it’s a shame to ignore them when a simple conversion solves the problem.
A cheesecake out of a packet (I think that’s what you are describing) is not the same as the real thing. This was the first one I made baked too. Previously I did ones that faffed around with gelatine etc. they weren’t as a good. Don’t bother with any that use jelly as a base for the cheesecake part. They taste like jelly.