Indesign Letter Format Printing

1.I have completed my college magazine in letter format(8.5 in * 11 in).

2.Now when i am trying to save as PDF or print in a single page i am getting two sides in one page.(two side by side pages have become one page.)

i am not able to complete printing (The red part is missing)

(In Print->Setup->Paper Size , Custom is not shown).