If there is a gap between your pen and where it appears on the screen most likely there is an issue with calibration.
To calibrate an older style SMARTboard with different colored pens and an eraser press the two buttons on the tray at the same time and follow the calibration pointers.
To calibrate newer style SMARTboard with black, red, green, and blue buttons press the button with a cross. Follow the calibration pointers.
To calibrate a Promethean board hover the pen over the flame icon in the top left corner of the board until the calibration points appear.