I've just tried the sophiesew digitizing program, but I'm not able to figure out how to erase or delete a line I made on accident. Do you know how to do that?
This is old so the original poster might not care anymore, but for anyone else that finds this post while searching:
If you're talking about an outline, go to the nearest green square, hover over it until the [Ctrl] text pops up, right click, and select "Split outline". Do the same thing for the green square on the other side of the line you want to get rid of. Now, when you go back to object mode, you can select that unwanted segment by itself, then right click and delete it.