Not sure if it's the same as my later plus 4, if so the catch on the B post/ frame is adjustable. I slackened the two bolts just enough to be able to move it in a tad, just tapped in by a bit of of wood and a hammer.
Nip them and try the door again before tightening fully.
There is movement up and down as well as in and out so try not to lose the starting point or you'll end up fiddling a while to get it right.
Not sure I've explained it very well!
