Had the same problem at one time, though not as pronounced as you seem to have. The solution was: 1) loosen the screws on the striker plate and slide it was far as you can in the direction needed - tighten screws; 2) loosen the screws on the lock assembly (inside) slide it around, trying to get the deadbolt to engage; 3) if that solves the problem tighten the screws.
Happy Camping! ///// Richard D.
2006 4x4 Ford 250 SD / 2007 Flagstaff 827 FLS
One very patient wife and one furry child who travels with us. Forty-two years of trailering and camping, and I still have a blast.