How far does it project/recess on the inside? You may have it the wrong way round or you may have bought a 'too short' barrel.
The measurements of these type of lock is strange if you are not used to them. As an example, I think you can get something like a 55-55, a 55-35, a 44-35 etc
If you have the old barrel measure from the face to the centre of the nib from both sides. You may find one side is longer than the other or they may both be the same distance.