There are a few options.
1) You can sideload an app (Settings -> emable adb, then install adb on your PC and install) that allows calibration.
2) You can just do a restart and that might fix it.
Press N button and power button for 30 seconds and then let go.
Nook will restart.
3) Try to turn screen on and off a few times.
Do you have a screensaver?