Exchanging after 28 days?

So basically I brought a dress from warehouse about 2 months ago in a sort of coral colour for my prom; which is next week. I went on their website today and there's the same dress in aqua. I was just wondering if I'd be able to exchange it for the aqua colour instead. I haven't worn it once, it's brand new but it hasn't got the tag ( when I brought it there was no tag). I still have the receipt and it says ''For items without a receipt or where the return date has been exceeded, Warehouse will offer an exchange for an alternative product or gift vouchers to the value of the current selling price''. So hopefully I can but 2 months does seem a bit long doesn't it? :/