As the title asked, when I tried to use features in surfacing and I want to create a surface based on a single line from a sketch, I am having trouble to just select on that edge.

As shown in the pictures for example where I tried to use the boundary feature. When I try to select just one line from the sketch, it sometimes works fine and selects it as an open group as shown in picture 1. But most of the time it selects the whole sketch and gives me the error as shown in picture 2.

I have no idea how I clicked differently to make it select either only the edge or the whole sketch. I looked at the selection manager but nothing there.

My question is how can I choose to select only the edge of the sketch and not the entire sketch every single time. Thank you!

Sample model is attached below.