Clicking the "And back" button will retrace your entire route (ie. doubling the distance), rather than the shortest way home.
If you are snaking back of forth around a couple of blocks, you will need to trace the entire route. Some of these mapping programs don't like you placing 2 way points on top of each other (which sounds like it may be the problem?) - zooming in a bit more will allow you to place the markers seperately, without distorting the distance.