i recommand using Drastic emulator, its one of the best emulator for nintendo ds en android,
why ? well, back in 2014 i was a beta tester for Drastic emulator, and i was suprised, it wasn't like ds boy or NDS4Droid, since all thos emulatore use the same developement code. but Drastic was close source code developement from scratch
and with Drastic, if you are playing a Ds game that use one main screen, you can go to setting and view it full screen, or you can use other screen adjustement .
just search for Drastic emulator on youtube and you can see different features of this emulator
you won't regret buying it,.