Tiling for poster printing is only giving me half the image

I have sheet music downloaded which is A3 format with 2 pages on one A3 page (it was the old way of getting a booklet to print), and none of my students have A3 printers, so I want to print-to-PDF in a file that, instead of 13 A3 pages, has 26 tiled A4 pages.  I have tried several settings and each time it spits out 13 pages, all of them are the R side of the original image.  I can't get both the left and right side of the A3 image.  What am I missing? 

Here is what I am doing:

1) original file page size is A3 landscape, my printer setting is A4 portrait -- in the preview, the greyed out portion is the R side of the A3 page, but at least it is one exact page in the A4 format I want, so it is placed correctly.

2) Actual size is selected

3) In the Poster part of the Page Size & Handling section, tile scale is 100%, overlap is 0 (which should cut the page exactly in half?) and I have clicked "Tile only large pages".

After printing, the output is only 13 pages, and each page is only the R side of the original image, so I have only half the pages I need.

Thanks, Becky