This is the little arc on the smaller camper I am designing and I am new to SketchUp and have failed to complete the task in my research in so of searching I cannot find anything that I one and understand and two that actually completes the task with some slight ease.
I have checked all the connection points and they are in line…
It’s difficult to tell for sure, but that looks like a horizontal piece attached to two vertical quadrants. If so, delete one quadrant and the top horizontal piece and use Push/Pull to extrude the remaining quadrant.