Oh no what's happened to my screen, went to chrome, went back and my model screen as this

oh no what’s happened to my screen, went to chrome, went back and my model screen as this, i have my model on here i need it, how do i fix, i literally don’t know what happened

You could’ve accidently maximized an area, “timeline” in this case. Hover over some area and press Ctrl + Spacebar OR Ctrl + Alt + Spacebar. Same thing to revert back.