I don't know the politics in your office, but one reason for writing down the ticket numbers could be to track the money and make sure they either get back tickets or money and that no one pockets the cash or attends for free.
Since they gave you the option to bring back the tickets, I'd do so, but I'd do it close to the deadline, so it at least looks like you made an effort to sell them, whether or not you did. In general, I'd go with the just say that you don't sell things, but it would seem odd to do that a day or so after getting the tickets. It would look like you changed your mind halfway through, rather than weren't quick enough to say no initially, even though that's not the case.
If I knew anyone I thought would like to attend, I'd ask them if they are interested, and then, if they say yes, mention that I have tickets for sale if they do, in fact, decide to go. I'd make it very clear that this wasn't a case of trying to make them go, more along the lines of if you are going anyway and haven't bought tickets, I have some to sell.