If you have one, call your coordinator. Did you have to sign-up in a book? i know when our church has done an Angel Tree or something similar, that there is someone at the church who keeps a book with all the recipients' names & the donors' names.
If you have everything off of the tag but the code, maybe you can call the actual agency who is coordinating everything, describe the info you do know and maybe they can help you?
Look in your car(underneath the seats, on the floor, etc.), look in *all* the pockets of your coat/jeans, look in all the pockets of your purse. Where's the last place you remember seeing the tag? Go there and close you eyes and calmly think.
And say
"Tony, Tony, look around
What was lost must be found.
Yaaaaaaaay, Tony!"
(Saint Anthony is the patron saint of lost things.
Good luck,
agnes!