I have not built the 1/48 version, but I have had this problem with other kits in the past. If you have not joined the fuselage to the wing assembly yet - you may be able to cut a section (or several sections) of sprue so that they span the opening on the bottom of the fuselage and spread it apart a bit to help make the bottom of the fuselage wider where it joins the wing.
I'm looking at the 1/72 version of the Airfix kit that I was working on last week. (at the same point of assembly). If the 1/48 kit is laid out the same as the 1/72, then I think there may be a little room for one of these "spreading beams" at the front of the fuselage hole, just behind the leading edge of the wing, but in front of the recessed gear bay. It looks like there is alot of room for a beam behind the recessed gear bay.
It doesn't look like there is any room at all for a beam in between the cockpit floor and the recessed gear bay.
Hope that helps. Before you know it - you'll be Dr. Zar - Styrene Surgeon !
Be sure to post pics !
Chris