If you want a mana GUI, call Minecraft.getInstance().setScreen(new ManaScreen()); somewhere display your GUI. I would recommend creating a keybind and listening to key events, and if your key bind is pressed down, running that code.

You are creating an entire new screen, or GUI. What you probably want is an Overlay.

I fixed it

https://mclo.gs/46Xf7Sq thanks

That seems to have fixed it, thank you!