I suggest that you THROW AWAY that L298 driver and buy a modern current driving microstep capable driver such as a DRV8825 on a breakout board from Pololu for example.
The motor is OK, it can be driven bipolar by connecting the ends of the windings to the driver outputs and leaving the centre tap disconnected; or using one end of a winding and the tap and leaving the other end disconnected. Follow the instructions on the Pololu website about setting the coil current, there is no need to set it very high unless you need a lot of torque. Don't worry about the stepper coil voltage, when you set the current right the driver will take care of it for you. Make sure you provide the capacitor near to the power pins that Pololu recommend.
Lots of good advice above about how to run the wiring.