Don't give up HM, all of the Sammio bodies - G46, Cordite
and the Spyder need a considerable amount of builder ingenuity to make them fit, work and look good, with the payback being the unbelievable affordability compared to mainstream(!) alternative kits.
Most of us who've successfully built them seem to have embraced that ethos, but, at risk of offending some builders, we also seem to be creative eccentrics, often with an engineering background, who see the little idiosyncrasies as challenges to overcome instead of headaches.
Those nicely integrated tail lights and the progress you've made so far on what appears to be Sammio's second least developed car (after the banana shaped Cordite) suggest that you might just fit the mould too.
Keep tackling those little jobs, inject some individuality and passion into that fibreglass body and it'll be finished before you know it.
See you on the road soon.