More semantically than some other answers, GNU software is generally on Linux computers, so if GNL was Not Linux, than it would be even more confusing for it to be on a Linux computer.

I think if you need to make the destiction, GNU+Linux is probably the best option for the whole software set and kernel included and if you want to talk about the operating system, I think naming your distribution and following it up with "a distribution of Linux" would be the most accurate, if you are in a situation where accuracy counts.

I use Arch, btw.