Have you checked your personal dictionary to see if you've accidentally added that?

Not entirely sure how you do that as it will depend on the keyboard you're using. If all else fails, you can maybe reset it by clearing the cache and files on the keyboard app (wild guess, but some clever person on here will probably be able to give you an informed answer).

 

What keyboard are you using?

Either way after you type the two words listed of hitting enter, press the proper auto correct/suggestion at the top. After a few of them it should remember it.