Mapping narrow passage

The end of my lawn narrows into a passage about 1m across. My x430 can get in to it but there’s no space to turn, is there a way to get it to mow down to the end, and then reverse out? Right now I can’t map it as you can’t reverse while mapping, just erase the border.
I also tried drawing the new border but it just turned before it narrowed and didn’t go down to the end.
So far, I’ve just been mowing it every few days with controller mode.