Could be too much fertilizer.

How often are you watering?

I've seen gardenias do this all the time. You take them home, and the buds turn brown and never got to flower stage. I have the same thing happen to my stephanotis that I just bought from Home Depot. It had many white buds when I bought it, got it home and the flowers never opened and they just fell off. I noticed that the same plants did this in the HD store too. Guess I won't buy those 2 again. Not worth it. Sorry about your plant.

Why cant people just type the words " pot shock " on a pubic plant growing forum ?
Okay a sudden blast of fert in a new soil may of done some damage but what should one expect a gardenia to do when they re-pot in a newer soil during it's flowering cycle ?
On a side note: You dont have to be sorry steel personal feelings or emotions simply dont grow plants.

This is what I would have done. I would have repotted using new soil without adding any fertilizer in the soil. Feed the plant by applying the fertilizer on the soil and then water in the fert. Do not use acid fertilizer. In any case, it's not a good idea to feed plant that you just bought as they might have just been fed.

anrev1719 - I hope your plant recover soon! I'm a brown thumb when it comes to gardenias and jasmine. Heck I kill everything except plumerias. Go figure!

Still every year around Mother's day I would try again. So last week I bought two Gardenia Standards from Armstrong but I'm too scared to plant them in the ground or re-pot for that matter. So for the last week they sat under the covered patio with some indirect light. I did moved them out to catch some rain on Monday... but I have not watered them again since. Both are blooming like crazy but with some yellowing of the leaves from below. I hope I don't kill them! :(