Thank you all for the replies.

I also figured that sanding would be the best option, so I already started yesterday. It looks a lot better and is actually not such a difficult job.
I still have a tiny gap on one side in the middle and am not sure how far I can go with removing material. On some spots I can already see the next layer of material, mind you, it is a very thin layer. It is not the strength I am worried about after removing material, but the front of the wing has a sort of dowel pen that fits in a slot of the fuselage. If it gets too thin it might get some play. But I guess I can also fix that so figure it is best to keep sanding until I have a perfect fit.

Rg,

Filip