When you can only see one screen on your classroom computer. You need to try these fixes.
1. press windows button (bottom left next to ctrl), and P – this will give you 4 options, one is to clone your screen.
2. IF this does’nt work then click on the windows icon bottom left, and click on your username. this should show if you have more than one user logged on (also works with no sound to pc.), please log the other user out.