Hi Steve,
I've just read the pages to this excellent build. I hope I'm not too late regarding the gap at the wing root which is quite obvious and apparent in many larger scales. Unless the manufacturer has provided a dehydral sprue support for the lower wing, I rarely follow the lower wing as a guide but look at head on image references for the dehydral. The Spit has a very pronounced dehydral following the images I have attached...
View attachment 1281915
View attachment 1281916
I would remedy creating the dehydral using masking tape, taped to one end of the wing tip and pulling it across over the fuselage and taping it to the other tip, pulling as taught until I get the dehydral degree per reference. Glue the wing root in place and fill any remaining gaps with epoxy or CA. CA has great tensile strength properties.
Do you have a straight frontal shot of your Spit. The side shots seem to show a straight wing...I could be wrong. If I'm too late for any corrections then leave it. It still is a Spitfire from any other angle.
Cheers,
Wabble