How do I print two A5 documents on one A4?
Solution 1:
Choose File -> Print. Select "Two page per sheet" and then press Print.
Solution 2:
In my experience, it's easier to convert (or Save As) the document to PDF at full size, which in this case would be A4. Then print from that.
In my experience PDF offers you far more options than most of the MS Office Suite, although I don't have 2013, so I can't say for sure. I often print handouts, and PDF > Landscape > 2 Copies Per Page works for me every time. In your case, I think the border is causing the issue.