yes, I think tail-gunner nailed the problem...
it seems like your front is completely "hollow" with no support.... (other than the control panel part...)
what I would do is cut a piece to fit into the front....
(like tailgunner suggested... but no need to cut the hole yet..) and just duck-tape it to the front temporary and then try it again....
are you going to have a coin door ??... if so....
or maybe what you can do is...
that front piece is a door itself....
since 1 side has the hinge....
and the other side... use some kind of clamp or lock so that the front door can be secured and add support to the whole cab...
then you can open the coin door to "unclamp" and open the whole front door....
I hope you understand what I mean...
