Sounds like you have the wrong control software loaded. One version (Forklift_B_L-throttle_R-steer.json.json) uses two different joysticks and one uses only one (Forklift_A_L-joystick-only.json) with steering and speed on two different axis. I would expect your behavior if using the wrong one.
See the bottom of the Makerworld page
To download the JSON files.