50 miles by definition isnt a newbie ride. Keep ur rides 20 or shorter for true beginners.
If you actually want to ride 50 at your pace make sure you have prearranged for at least one other rider you know will stay at your pace. With a nucleus of slower riders not all will be pressured to hang with the fast guys.
If you didnt have any such partner prearranged, reality is that despite your intent, you werent prepared for your own ride if you were blown off the back all alone.