Everything's going according to plan. Check out Youtuber Sariel's review on your set HERE.
At about 26mins in, he addresses your concern. He notes the looseness of the feet when fully deployed, and says there are 4 pads stored in a compartment over the front axle. Just build on.
Depending on what you are planning to do, there are several options. @Rin Rio-Oki showed solutions for when you are planning to build a fence-like structure, but if this is supposed to be a solid wall, here are three options:
The option furthest back is where you use a 1x1 brick with side stud and a tile in the corner. You could alternatively replace one of ...
Here's an attempt at what I think you might mean, an offset wall that turns a corner while somewhat maintaining it's aesthetically balanced negative space between the bricks.
I'll upload the build file, if this is what you're looking for.
(Of, course we're focusing on the wall not Picasso's Junk Lighthouse behind it.)