Double recipe in half sheet pan?

I'd say doubling should be ok (I usually have to test thoroughly!). My 9x9 is 81 sq. inches, so doubling that would be 162 sq inches if I had two 9x9's next to each other. A half sheet pan is 18x13 inches for a total of 234 sq inches. So you should theoretically have plenty of space there, even with any scrap dough (there might be a little).