Games playing in a small window

New user here. I have searched the forums an am not coming up with much. Im trying to play games and strangely most games go into a small window. I go into the resolution and set it yo different things and always get way too big or way too small. im playng on a 4k tv that i have my pc's resolution set to 1080p because none of these games are going to be close to 4k. How do i make the games fullscreen? sorry if this is a noob question but im kinda new to the emulator scene

Hello, and welcome here.

Have you try by using BatGui (at the root of your RetroBat folder) ?

Hello,
Is retrobat interface in fullscreen ?

Can you screenshot what you mean by 'in a small window' ?

Also please select an avatar