A couple of times I have set the parking brake and forgot to release it and drove the tractor. My mind was on something else.
My question... Did I do any damage ? Any way to check ?
You did no damage. You had no brakes in the first place. You can set the so-called "brakes" on a BX and use the thing for days with no great impediment. Eventually you will realize the brake is on...The brakes on all the BX I ever operated (6 or 7 of them at least) are utterly worthless. I am fairly sure I can stand in front of the tractor and hold it back (using both hands and good tennis shoes) from motion with equal or better effectiveness than the so-called brakes.
My own BX2200 (I've had for 25 years) has the high brake pedal right above the "go forward" end of the pedal for the HST. MANY times I have goosed the thing suddenly forward while intending to hit the brake. Terrible design. When I do succeed in using the brake it amounts to a minor slow-down, like you were pulling an extra load. On a barely sloping driveway you can park the BX and set the brake as tight as your leg allows. It will stop the tractor from coasting most of the time unless the driveway is steep. If you have some need to actually stop serious motion in EITHER direction the only real brake you have is the HST pedal (hitting reverse to stop forward motion. And that only works when the motor is running...) These are wonderful little tractors that can do amazing things but braking is not one of them.