Hello tripmaster,
Your wiring seem to be good so I think that is your code that is bad.
If pins 5 (In1) and 7 (In2) of the l298 are at the same level the motor stop quickly. If they are at different levels, the motor turn in one direction or the other.
If the pin 6 (Enable) is low the motor don't turn is "free" (I don't know how to say "en roue libre").
summary :
Enable : LOW -> Nothing
Enable : HIGH :
In1 and In2 : LOW or HIGH -> Quick stop
In1 : LOW and In2 HIGH -> the motor turn in one direction
In1 : HIGH and In2 LOW -> the motor turn in the other direction