Turn off built-in display when using external monitors

Hi Apple Community,

I have a dual monitor setup for my MacBook Pro. The two monitors I'm using are a Samsung monitor and an iPad Air 2 running Duet Display. The setup works well, but there's a small problem. I keep my MacBook open so that there's ventilation and I just turn the brightness down to zero. However, the built-in display is still being read as a third display. This is causing a problem because sometimes my programs open in the unused display, and I have to turn the brightness up on my MacBook, find the window, bring it to the main display, and turn the brightness back down to zero. What I would like to do is turn off that display completely while using my other two monitors.

I know that closing the lid of the MacBook is the simplest solution, but then there isn't as much ventilation. Plus, I do game development on it, and that can make the fan run. Is there a way I can turn off the built-in display on the MacBook Pro without closing the lid so that it only reads the two connected monitors? Any help would be much appreciated.