I triple tap the power button and it still won't let me out of Guided Access

When you are stuck in Guided Access mode, you can be really stuck as the typical triple tap on the home/power button to quit out of Guided Access may not work. Even a forced exit won't work because the power button and the home button are disabled. 

The only way to get out of Guided Access is to perform a forced restart - forcibly rebooting your device. Once your device is restarted, you can then go to Settings > Accessibility > Guided Access > Guided Access - and turn off Guided Access if needed.

Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)

Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.

Use Guided Access on iPad - Apple Support

Use Guided Access with iPhone, iPad, and iPod touch - Apple Support

If a hard restart doesn’t work (and only if it doesn’t work because it can affect your battery) you can let the battery get to “0%” and once your iPad has been plugged in you should be out of guided access.

It’s also possible that the person you turned guided access on for tried entering the incorrect password too many times and your locked out for a few minutes or hours

Kastaspella wrote:

If a hard restart doesn’t work (and only if it doesn’t work because it can affect your battery) you can let the battery get to “0%” and once your iPad has been plugged in you should be out of guided access.

Never (ever) deliberately fully discharge an iPad battery. If allowed to remain in this state, the Li-ion battery may never recover.