OK, first things first. The seat bulkhead appears to be the correct one for a razorback, so that's good. BUT ! It looks like you might have fitted it leaning slightly to the left, when viewed from the front, although it might just be the camera angle/ wide lens making it look like that. Check it, as it'll need to line up perfectly with the leading edge of the rear of the razorback.
Next, if you mean by 'arch' the forward end of the cockpit of the razorback, where it goes over the instrument panel, then yes, line up on there. But you'll need to either hollow out that 'dish', and add frames, or build it up to form the coaming, like in the pics I posted.
Finally, where the rear openings are, in the side of the razorback, immediately behind where the seat and bulkhead go, should have concave 'walls', as you can just about see in the oic of my old model. If the kit doesn't provide parts for these, just fit some card, inside the fuselage, to blank them off, lining up with the seat bulkhead. Now you know why that has to be straight and 'square', otherwise nothing will line up, and the canopy won't fit, open or closed!
Hope this makes sense.
I don't think fitting the razor will be too bad, although you'll probably need some filler along the joints. Just ensure this is smoothly filled and sanded flush, with no lumps or bumps to give away the joint!