Just switch the wires and it should go the way you want it.
The battery may be connected correctly, but did you reverse the motor connections by mistake? The battery will need to be connected the correct way for the electronics to work, but the motor shouldn't matter, it will simple go in reverse if you've connected it wrongly. Try reversing the motor connections but leave the battery connections alone.
You either have the battery connected the wrong way round, or the motor improperly installed. If your motor electronically controlled, then the chip may be fried.
+1, lol, +1, +1, +1 for the answers below
swap the battery round or connections from bettery!
The caps-lock key on your keyboard is a wireless reverse switch for your motor. Turn off the caps lock, disconnect and reconnect your motor, and it should work perfectly.
That's because today is Backwards Day! ;-)
In the classic sci-fi vein: "reverse the polarity", i.e. swap the battery connections. L
If you truly have the battery connected properly then You have it in reverse gear, There is a reversing switch that is in the reverse position, Your rechargeable batteries have taken on a reverse charge, You are running an ac motor off an inverter and the starting capacitor is installed backwards, There has been a cataclysmic event that has reversed the poles of all magnets in the world, OR, You don't really have the batteries hooked up properly.