Purchased new speakers - did I make a mistake?

[basite]

What he said. There's nothing wrong with using full-range speakers for surrounds. Just think -- you'll be able to listen to that Blue Man Group full blast! (Or any other "aggressive" surround mix, where they put a lot of material in the rears.)

or a big explosion in the rear...
or anything else where the rear speakers get alot of signal.

there's nothing wrong with using big speakers everywhere...
heck, I've even seen people who used 2 more big floorstanders as a center...

Rock on,
Bert.