How to make a fast wall follower robot using Vex Robot System

I want to make a simple wall follower robot, using 1 ultrasonic sensor on the robot left side, 4 of 393 motors, 2 of 2.75" omnidirectional wheel, and 2 of 2.75" high traction wheels.
Using EasyC I make a very simple program, with the distance from wall 4". At the first move the robot can have the right correction to the wall. But the robot will be error after that. It seems like the Vex Controller have a lag response due to the sensor reading.

Hope any advice. Thank you

To start, I would recommend posting your code here. Even though I am not an expert on EasyC, there are many people on the forum who are.