Nope you did nothing wrong.....Just try it again after you get it re assembled. I usually slide the rear of the chassis in at angle at the rear wheel openings and then slide it back as far as it will go...usually the rear wheel wells will fit inside the body at that point. Then bring the chassis slowly down until the next part hits...thats usually at the firewall. gently stretch the body out to allow the firewall to go in (sometimes a flat thin blade screwdriver helps or a exacto blade even to shoe horn it in) you might have to raise up the rear of the chassis a bit help and maybe slide it front to back some also....once you get it all in you can slide it front to back to get it on the right spot. Just take your time...it will go.....and sometimes you have to put the front half of the chassis in first so if you started at the rear last time maybe try the front half this time...you will get it.