The funny spelling of centre always gets me too, it just looks so wrong! I can get used to writing words that end in ise as ize, and colour as color. But center, fiber, liter, etc just don't sit right.
Maple not Mapel
Cable not Cabel
Centre look and sounds like “cent-ruh” rather than the rolled out sounding of err sound to make “center”. Then again, how you say it is a bit different, too.
The first is much closer to the British pronunciation, which (I think) is much more deserving of the spelling "centre" than the second "cener".