Sometimes those valves do get stuck. Try opening and closing the valve several times, back and forth, each time with a little more force. It should take maybe 3 or 4 pulls like this and the thing should open fully. But, don't pull so hard you break something. You just want to work the valve back and fort and any obstruction will work it's way out.
If that does not work, then your camper is still brand new and under warranty .... you know what happens next?