You can try resetting the device putting it in recovery mode, hold down the home/power button on the side until you reach the “rebooting” screen, then let go and press the home/power button again when on the “rebooting” screen. After this, you’ll get to a page that has red text you should be able to use the home/power button to scroll down to “recovery mode” and when you’re there hold down the home/power button. This will reset your device to factory state and allow you to use your watch again.