So, your plant produced 1 bud/flower and it set a fruit. A tomato plant should produce dozens of buds/flowers and MANY of them will produce a fruit. What I think is happening is mainly not enough direct light followed by too much nitrogen. Nitrogen produces foliage but without enough sunlight photosynthesis cannot be maintained, thus limited foliage is grown. Secondly, too much nitrogen many times ties up or reduces the amount of P and K a plant is able to uptake. P is what determines buds and flowers on a plant. If the P available as uptake by the plant is reduced there will be few or zero flowers and thus no fruit. I would get another grow light and run both lights 12 hours per day and after a couple of weeks if no buds start to show reduce the amount of fertilizer.