How do i get my spell checker to stop making me spell things like a Brit?

I've been using "After the Deadline" for some years and it uses only American spelling. I've had to use my own judgement. Since I switched to Chrome (from Firefox) the spell checker has switched to British English. I guess it's Google's own checker.

I think Chrome would do that for you, too, if it knows that you live in the US. 

Change the dictionary that's used for spell-checking. 

Lol! Usually it's we Britons (not "Brit" please... - possibly invented by British tabloids' headline-writers) complaining about their computers determinedly using American spellings.