The other day I also read the post regarding gift card to the teacher. $100 is a not big deal; that is what we have been doing each year for each teacher, of course at the holiday season. It is not a good idea to do it right before asking the teacher to do something; getting along well with the teacher and making a friend witht the teach since the beginning or the year before.
Again, $100 is not a big deal. My gut feeling is just forget about it and let it go. I do not think the teacher will care too much about it, as long as he/she truly recognize the achievement of your child. Think in another way, declining the gift is the sign of being decent; a decent teacher should not be disturbed by this small accident.
My 2 cents.