Buy a new tank, your really gonna regret it if once stocked, it splits and you lose everything. I know it sucks, and is added expense.. If your just starting out i would strongly advise you to really think about the shape, overflow method, area etc of your new tank as its a huge problem if you decide to change down the line.
My 55 is a cube and its made out of 12mm glass (just under 1/2"). Acrylic tank are usually made thicker than the equivalent size in glass, so imo 6mm is far to thin, and is most probably intended as a reptile tank. Also be aware that acrylic does scratch much easier than glass, get some sand between you mag float and the tank and you have a problem.
Hope this helps..