Baby not sleeping enough

Caitlin • Married on Halloween 2015 👻, expecting our first baby Aug.17 2016!
So I tracked my son's entire day yesterday on glow (sleep, diaper changes, feedings, etc) and I'm feeing really worried because he's only sleeping about 10.5 hrs a day. 😞 I know babies are supposed to get 15-16 hours a day so I'm feeling really worried. Anybody else experiencing this or have any advice?