My wii fit board keeps telling me to step off and press (A) even though i am not stood on it

It is not a problem with syncing. It has to do with one of the corner sensors. I have repaired many in the past with this problem and 98% of the time, the screw inside of the board on the foot closest to the orange and white stick was too tight causing the sensor to always be on. The other 2% is most likely some damage with the circuit board which would require a repair from Nintendo.

The Repair:
with the board on and synced, go to the training menu and enter the part of the game where it tells you to step off and press A. Flip the board over and with a phillips head screw driver, unscrew the three screws around the foot I mentioned above. Remove the pieces and you will find a large Torx T30 bit under that holds a metal plate to the top of the sensor block. If you don't have that, a Flat head screw driver that fits in the slot will work. Slightly loosen that screw. Just enough so that its a little looser but not too much because it will cause that side not to function at 100%. After doing this attach the foot and plastic piece and screw the three screws in most of the way. Flip over and press A and the system should go past the error. IF not repeat the steps with little adjustments until the problem is resolved. It is not a problem with syncing. It has to do with one of the corner sensors. I have repaired many in the past with this problem and 98% of the time, the screw inside of the board on the foot closest to the orange and white stick was too tight causing the sensor to always be on. The other 2% is most likely some damage with the circuit board which would require a repair from Nintendo. The Repair: with the board on and synced, go to the training menu and enter the part of the game where it tells you to step off and press A. Flip the board over and with a phillips head screw driver, unscrew the three screws around the foot I mentioned above. Remove the pieces and you will find a large Torx T30 bit under that holds a metal plate to the top of the sensor block. If you don't have that, a Flat head screw driver that fits in the slot will work. Slightly loosen that screw. Just enough so that its a little looser but not too much because it will cause that side not to function at 100%. After doing this attach the foot and plastic piece and screw the three screws in most of the way. Flip over and press A and the system should go past the error. IF not repeat the steps with little adjustments until the problem is resolved.