I need to print, sign, and mail my 2018 return. I downloaded the amended return software but when I amend and print, it does not print with the signature box.

It doesn't print the bottom of page 2?  Did you print page 2?

In the FILE tab choose to mail in the return and the forms & instructions will be presented in the PDF. 

Are you filing an original 2018 tax return or an amended return? Form 1040 for 2018 prints two half-page forms on one page. The signature space is in the middle of the printed page. On Form 1040X (an amended return), the signature space is at the bottom of the second page.

If you are just filing an original 1040 ( even if you are using the amendment program) then the signature place is on the page 1  ... however both page 1 & 2 are printed on one page by the program to save paper ...

Thank you very much. I was looking at the bottom. Really appreciate your help.