How do I stop Blender 2.8 from creating extra faces when I just want to stretch pre-existing faces? I'm new to blender so I'm sorry if this is a noob question. Here is an example of what I want to happen when I click and drag the face along the Y axis (represented by the green arrow):

From this:



To this:



However, two extra faces appear when I try to drag along the y-axis:



Here's the face I'm stretching along the Y-axis:



Any help at all on this would be greatly appreciated. If you need more information I'd be happy to give it to you. Thank you all!
You must have overlapping vertices. Before pulling the edges, select all (A) and altM > Merge By Distance to make sure you've deleted those vertices (check the Operator box on the bottom left of the 3D view to play with the threshold)