Is your interior tub squarely seated? It appears your chassis is being "pushed" rearwards, both front and rear tires are nearly touching their respective openings at the backside. This kit is a very old molding, and has its share of problems, BUT they can be overcome. You might need to file a bit of plastic away from the front side of the rear wheel wells, and/or from the bottom rear portion of the interior tub (see where they touch, at the seat cushion area?). Also, check those round "holes" that locate the interior tub, behind the rear package tray. You may need to file them back into a better version of "round", again, as this is an old molding. That should help bring the chassis closer to center in the wheel openings, then you can judge other fitment issues more accurately. Adding plastic pieces to the inner fenders is pretty basic modeling stuff, but if this is new to you, don't be afraid to tackle it! I would locate some stiff paper to use to make patterns, then use those to make custom fit extensions to hide that space that bothers you in the wheel well. ( I like 3x5 index cards for drawing/cutting patterns. Manila folders also work well.) This saves your valuable plastic, as paper is easy to cut, re-cut, and fit as much as needed before tracing onto plastic sheet. The support you want may be as simple as a short stack of small squares of sheet plastic, or trial and fit stub of sprue attached to the top of the front inner fenders, so that they contact the underside of the horizontal, flat part of the front fender. DRY FIT EVERYTHING! Time spent now will reward you with a satisfying stance. We're all pulling for you...