If you want to restrict access to other apps on the iPad, and do not have a kiosk enclosure that covers the Home and Sleep/Wake buttons, you can disable them.
(Please note that if you're using IOS 12 that this feature will turn the screen off after 20 minutes of not being used)
How to Disable the Home and Sleep/Wake Buttons
1. Launch the Settings app.
2. Tap Accessibility.
3. Scroll down and tap Guided Access.
4. Enable Guided Access.
5. Tap Passcode, and set a passcode for the Guided Access settings.
6. Return to QuickTapSurvey and launch your survey.
7. On the first screen of the survey, quickly press the Home Button 3 times.
8. Tap the Options button under Hardware Buttons if you'd like to Unable or Disable Sleep/Wake Button and Volume Buttons.(The default option is disabled)
9. Press the Start button at the top right of the screen to fully enable Guided Access.
Your Home Button, Sleep/Wake Button, and Volume Buttons are now disabled.