Think I messed up

If the dealer said you could haul 11k, than they were wrong. They should be willing to cancel the deal and allow you to pick an appropiate trailer. If they balk about it, you may want to consult a lawyer, or contact the attorney general's office in your state. Personally, I wouldn't think of towing something that long and heavy with a 1/2 ton truck. I'm towing just a little over 6K with a Tundra, and wouldn't want to haul much more....especially for any travel through mountains. Unless you can afford to upgrade the truck, you don't want to buy this trailer. If the dealer won't cooperate, contact a local news station that has a consumer help service or whatever it's called in your area.

I hope you get some cooperation and get this resolved properly!