Geeze, I've always "stretched" the truth. :B
Actually a lot depends on the site itself whether or not you will fit.
I've been to sites that were advertised to only accommodate a coach my size. Once I got there I found that if I backed up and allowed the rear overhang of my coach to extend well past the paved portion, there was plenty of room for a much larger coach. On the other hand, if there was a tree located at the end of the pavement, that same site would only be able to accommodate a coach the length of the pavement.
I guess if you do not tell the truth as to the exact length of your coach, you run the risk of it not fitting when you get there. They may or may not be able to accommodate you, if there is another vacant site available.