MasterAlex,
Take a deep breath, it's not as bad as it looks. I had a similar problem on one of the SSE's that I've built. The first part of the problem was the wing tube (the metal one) was just a bit too long. It didn't allow the wing halves to fit down flush on the side of the fuselage. So check that first. If needed just file a little bit off the end of the metal tube.

After you've checked that now see how the wing halves butt up against the side of the fuselage. You may need to do a little bit of sanding on the root rib to get it to fit flush. The reference point that you'll need to pay attention to is that the leading edge sits at a 90° angle to the side of the fuselage. So sand down the root rib a little bit so that it sits flush up against the side of the fuselage.

Hope this helps

Ken