OK, do you want the edge(where the binding will attach)to be straight but the zigzags to look as they are going into it?
If so I would cut enough tumblers from your border fabric so you can begin and end each row with one. trim the outside edges and attach the top and bottom borders. The sides will not be a one piece border but should look like it.
Not sure if this method is really worth attemting since the top is already finished but you could try it for the next one.