I am newish around here and I am sure that others more experienced will chime in.
The gap could be filled with shims from wood veneer depending on its width.
The veneer is very thin (1 mm) and available on ebay (depending where you are).
As to the gap, that looks a bit grim.
If you are doing a solid colour you could fill it and then spray over it.
If however, you want to stain the wood then it will be visible.
Depending on your location returning the body/kit might be an option.
Email Adam and see what he suggests.
Cheers, FB.