5ColorRainbow

hello! this is my first time trying to burn a DL DVD and i'm having a problem i use a blank Verbatim DVD-R DL 8x (8.5Gb) and the image file is about 7Gb. but it keeps saying that there's not enough space on my dvd no matter what burning softwares i tried (Nero, Ashampoo, ImgBurn) here is what it said what should i do abt it? thanks in advance!