I don't think the interior tub is too short, well maybe a bit, but not much, the real car doors open to reveal a bit of the rear inside trim like what you see in your picture. Google it and see, but what you've done so far looks great! Here's a resin Falcon body I'm doing, although it's not quite as noticeable on cheap early cars, you can see the outer door skin goes further back than the interior rear side panel.