We're not saying you're trying to trick anyone, but we are saying it's highly likely that you've been tricked.
I assume it's the coin on the left, with "2007" date on both sides? A different date on the two sides would be a clear indication that it's not a genuine "mint error".
It's impossible in the normal course of mint operations to make a two-headed coin "accidentally", because the "heads" dies are differently shaped to the "tails" dies, and can't be "accidentally" mixed up when being inserted into the coin press. A double-headed coin can only be made "experimentally" by mint workers on a special press set up for that purpose. No such "experiments" can be officially released to the public; they're all supposed to be either destroyed or kept by the Mint. Any found in public hands would be considered stolen property, smuggled out of the mint by a mint-worker hoping for some "extra profit".
There are very, very few genuine, certifiable two-headed coins: two examples of a 50¢ from 1977 are known; when one was put on the market in 1984, it was confiscated by the Federal Police as stolen mint property. I believe both specimens now reside in the Mint Collection.
I haven't heard of any genuine examples of two-headed coins from recent years. Most of the ones you see on eBay or elsewhere have been "manufactured" as a trick coin. The usual way is to grind down one coin until it's wafer-thin, then grind out a second coin to make a bowl-shape, just big enough to insert the wafer-thin first coin into. When done expertly, it can be very difficult to detect the seam. It's safest to assume that this is in fact what you have, unless we can see very
detailed pics of both sides of the coin, as well as the edge. As rggoodie implied, the weight of such a "machined" coin is often wrong. It will also probably "sound" wrong when spun or dropped.
I should point out at this point that anyone making such a "trick coin" here in Australia would be deliberately damaging or mutilating Her Majesty's Australian coinage, which is also illegal and people should be discouraged from doing this to current Australian coinage (though I doubt the Feds would be too interested in prosecuting anyone for mutilating two 5¢ pieces).
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis