Gardenias are tricky to grow well for even the experienced gardener! They need bright light, high humidity, moderate and relatively uniform temperatures and an even supply of moisture and nutrients. Limpness or aborting of flower buds can be caused by too much water, too little water, too low humidity, insufficient light, rapid fluctuation in temperatures, drafts and even changes in plant location. Make sure irrigation water is not excessively alkaline - adding a few drops of vinegar per gallon will help. And use an acid lovers fertilizer when you do fertilize.

May be best to leave it be for a bit and let it recover from recent transplant. And try not to kill it with kindness. Sometimes less is more :-))

I'd consider that the fertilizer might even be a problem, along with the factors cited by gardengal. And if you've been placing it in DIRECT sun for a few hours each day, that could be a problem. Plants (all kinds) need to be introduced to direct sunlight slowly, starting off with shade or filtered light. We don't know what kind of potting mix you've used; some can actually make it difficult for the roots to absorb enough water.

By the way, I don't know what the temperatures are where you live, but gardenias are very happy to be outdoors in chilly temperatures.

When you repotted - has the new pot got excellent drainage i.e.generous size and number of draining holes?

Is the potting mix free of water crystals - those additives that 'hold the water'?

Has your potting mix got something like sharp gravel in it to improve drainage and aeration in the soil?

When you pruned back the roots - did you also take some off the top? Otherwise it may be that too few roots are struggling to get supplies to too many branches and flowers up above.

If your potting mix has slow release fertiliser added - you don't need to feed extra for a while (months).

While your plant recovers after the repot - place into a sheltered place out of sharp breezes, with good light for most of the day, but only about three hours of gentle sun in the morning, for three or four weeks, then gradually increase the amount of direct sun.

If it needs more humidity do the standard placing your pot on pot feet in a dish of water so that the water can evaporate but the bottom of the pot is actually out of the water.

If the wilting continues you'd be prudent to tip out the plant and check the roots/drainage. Some potting mixes can become awfully cluggy very quickly, meaning it stays too wet and with not enough air for the roots.