Hello all;

I'm getting some weird curling of surfaces when untrimming and extending them. I've taken some screenshots of my adventures.

The rectangle is the surface I want to untrim. I've taken it from a part model. The main block behind that surface needs to be flush to that rectangle.

When untrimming, the surfaces start to curl. As you can see by the right side of that now extended surface, it's starting to curl upwards:

When I trim out where the surface starts to curl, then try to extend the surface, it curls as soon as I try to drag the surface out.

Any insight as to what I'm doing incorrectly? I'm very much a solidworks nooby, so I appreciate any guidance.

Thank you, kindly!