I just downloaded this mod and I'm testing it in a 1.12.2 creative single
player world. I have successfully made an elevator but it said I couldn't use it because its not owned by me and I am in single player. So I removed the elevator with a stick as mentioned in the manual. Now I can't make a new elevator. When I right click one corner block and shift right click on the other corner block, it just sets that block as a new first corner block.

I tried making an elevator in a different chunk and the same thing happens.

I figured it out. I changed my key bindings and forgot that shift is the default for sneak.