Paste the AHK below in the Running AHK tab when you go to >Tools>Manage Emulators and edit Citra. The sleep time in the code is just due to Citra on my system opening with a slight lag so you may not need it. It will not cause issues to have it, but you may see Citra windowed first then fullscreen. So you can lower the sleep number if needed.
Sleep, 2500
SetKeyDelay, -1, 110
Send {F11}
Return