Hi Ro
These things can happen and we've probably all had our experience of them. What I'm not too clear about is the length of the damage. How far does it extend towards the tail?
The thing is not to get too disheartened. There is no easy solution, but what I think you need to remember is that this has been a fantastic build so far and you have achieved so much. With that in mind, the first thing I'd do is to step away from it for a day or two and then do as you say and fill, sand, reprint as a first option. As LM has said it might not be easy, particularly in matching up the green exactly. But you have two things working for you. First, if the white bands confine the damaged area they provide a natural boundary along the top surface avoiding adjacent greens. If the damage extends significantly towards the tail, you have a nice broad, flat area with vertical sides to play with. The second point is that if the most extensive damage is more localised immediately aft of the first stripe, then, even if you're acutely aware that it's there, the viewer is likely to focus on the Lewis gun which will also at least partially conceal things.
Should the restorative work not work out as you want, you at least then have the options of purchasing another or pouring your heart out to Revell and seeing if they would offer you some replacement spruces. Some of the big manufacturers can be hearteningly generous.
Best of luck with this.
Best wishes
Nigel