Technic 8071 assembly problem
This is the image from the Book 2, Section 14, Page 4 on the instructions from the Lego Website - source. Does yours look like this?

To me it does look like it's not quite right - if you lift the yellow gear out, move the second part into position and then put the gear back it in it looks like it might fit, although the yellow gear wouldn't turn.

I'd advise contacting Lego support, or see if you can pick out the way the person put it together in this YouTube timelapse video.