You may find that over time your reach gets a bit more just in the normal course of playing. In the meantime, or if it doesn't happen, you need to roll; plenty of pianists out there are in the same boat and get by OK.
Specific exercises to stretch your hand are much more likely to result in injury, sometimes permanent and irreversible. Many a promising career has been ended in this manner.
I don't think you can enlarge your hand span, some people just have small hands.
I have the same problem, I can only reach 9 keys if I stretch my fingers as far as I can. I'm practising on the Liebestraum from Liszt, and many chords I just can't reach, so I just play them as fast appregio's, and luckily that sounds also good in that piece, but it's still frustrating. I don't think you can enlarge your hand span, some people just have small hands.