SLUG Problem on a Smooth barrel.?

I recently tried 50yd shot at an range with Browning silver smooth bore 28" barrel with imp Cyl choke.My chamber is 3" and i did use high velocity 3" 7/8 oz. slugger rifled slug as well as 1 oz slug.It shot 5" and 4" high from the bulls eye.I did find the blast sound was more strong and it kicked like 300 win ultra mag.I'm more worried about hitting bulls eye than recoil.I was holding the shotgun tight and on shooting bags why would you think it shot so high ???Any Suggestions?????????