Are you using Anti-MicroX for your joystick and throttle? You can map the "Enter" button on your keyboard to the clutch button on the throttle. On the real test you will be pressing the clutch button.
Here's where the clutch button is:
View attachment 38673
I don't know if it'll work on your PC, but if you're using AntiMicroX, you can use the settings file I've been using before I took the test. I attached it below. It has all the needed buttons mapped already.
Were you pressing Enter on the keyboard during the real test?