Direction problems with servo library hindering field testing.

Other Hardware Robotics
1

I am nearly done with my project but since I had to use servoTimer2 instead of the normal servo library I had to use different things. I got my robot to turn left, right, and go forwards but since I am using something that turns the pwm into degrees I cannot go backwards. I just want to go the same speed as forward but I cannot due to the fact when i do the opposite of my normal forward function it just turns in a circle or really any other combination that doesn't go straight(90, 90, 45 and 45, 90 and 45.) but I have all the directions in my program except backwards which is an very important in terms of real life testing.
Here is my code going forwards(the delay doesn't matter I just kept it the same after I played with going left and right. )
Also, the 2 servos are continuous rotation servos from parallax.

// this sketch cycles three servos to 0, 90 and 180 degrees  

#include <ServoTimer2.h>  // the servo library

// define the pins for the servos
#define leftWpin  10
#define rightWpin 12 


#define degreesToUS( _degrees) (_degrees * 6 + 900) // macro to convert degrees to microseconds

ServoTimer2 leftWheel;    // declare variables for up to eight servos
ServoTimer2 rightWheel; 


void setup() {
  leftWheel.attach(rightWpin);     // attach a pin to the servos and they will start pulsing
  rightWheel.attach(leftWpin);

  leftWheel.write(degreesToUS(90));
  delay(950);
  rightWheel.write(degreesToUS(90));
  delay(950);
  rightWheel.detach();
  leftWheel.detach();
}

void loop()
{

}

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