My Bluetooth controlled RC car is not moving in a straight line

Hey guys, I am using an HC- 05 bluetooth bodule along with arduino nano to control 2 DC motors. The problem is. My RC car simply doesnt move in a straight direction no matter how much I tweak my coding. It either moves towards the left or rightI have already checked my wirings and motors. All are working fine. Please guide me. I have a national competition coming up in a week...

What did you do to make it move straight?

Have you forgotten to tell us something?

...and?

Do you have encoders on both motors? If so you can use the error between the encoder counts to drive a control loop to correct the steering.

If you don't have encoders you won't be able to correct this easily