Can't completely sync all PDFs from iTunes to iPad2 iBooks!

I can't sync all of my 126 scanned PDFs from my iTunes Books library into my iPad iBooks app...it maxes out at only 13 PDFs. Please help!!!

How large are the files? A scanned PDF can be very large and I wonder how much free storage you have on your iPad.

Tim

Thanks for responding! Files r small-just magazine clippings(1-6pages) 126 of them. In iTunes it's less than 100mb in total
Plenty of space have 16g left on iPad.