My take on the original sentence was that the curry can be made anywhere from zero (or one, or whatever) to seven on the spiciness scale, therefore you would need to retain 'made up to a'. Which is not to say that I'm right and you're wrong, but I think it can be argued either way.It is better to say "prepared" instead of "made up" and either using "a" or not is ok.
Uncle Bob, your memory may be slipping. It was "Oi'll give it foive".Isn't "a 7" an abbreviation of "a score of 7"?
It reminds me of a (dreadful?) pop music programme on UK TV in the 60s where the judges said things like: "I'll give it a five"