Hmm, how many pages long is the zine (counting the front & back covers)? And what are the page numbers of the two map pages (if the front is page 1)?
I think to get the map pages on the same spread, you'll want the first one to be on an even-numbered page & the second one to be odd. At 25 pages total, the ZineArranger is probably adding 3 blank ones to the end to bring it up to a multiple of 4. You could insert a blank page somewhere prior to the map to get it to land on 24 & 25--I think that would do the trick. Or you could add all 3 blank pages in somewhere prior to the map & have the map be 26 & 27, if you want it to be right at the end.