Also remember to do surface_resize(application_surface, 64, 64); to make the game actually output true 64x64! If you don't, it'll allow subpixels and stuff when you scale the window up
Viewing post in 64x64 , or 128x128 scaled?
The application surface was added so as to PURPOSELY ALLOW clean sub-pixel rendering for scaled up views, which is an issue is you want to keep 64x64 but scaled up. But seeing as you don't have an application surface in GM8, you simply don't need to worry about it. As long as you set the correct view/port sizes you should be good to go.