In my opinion, yes I do think you have too much soil. If your plants decide to get any bigger they'll run out of room. I'm pretty new to this too (I actually went out and bought some cookie jar containers like those to use for my own terrariums). But I do have two (so far) successful terrariums. Neither of them have too much soil. The bigger one might not even have enough.

The smaller one.

The first pic is of a chloryphytum and a fittonia and the second pic is about 6 fittonias - one of them a pink variety. Neither of them get direct sunlight. They're both placed on south facing windows, but get plenty of shade from the house next door. The bigger terrarium is sealed. From what I've read on here, there aren't many advocates for sealed terrariums. After opening and closing the lid for the first week or so and finding the right balance of moisture inside, it's remained closed.

I would agree that you have too much in the jars. One of things you could do is skip the bottom layer of gravel. Despite the "convential wisdom" it really does not provide any benefits. I would then further decrease your soil by 1/4 to 1/3. The problem with your current level is, as GT said, it does not currently allow for much room if your plants start to grow.

Happy planting!