Welcome to Goy. The one you have will grow to 10 feet if left untrimmed but the good thing about box is that it will stand hard pruning. It is popular for topiary work and there is no reason why you can't have a few topiary cones, birds or whatever cut from your shrubs once it grows up a bit. It is also evergreen. Are your white leaves hard and papery it could be it is needing to be watered more. The grass would have been better to have been removed so that it is not in competition with the hedge. Turn the lifted turves over on themselves in a heap and they will rot down, somewhere inconspicuous. You can then use the soil again where it is needed. Did you put anything in the planting soil like bonemeal which will help to establish your plants. Prune your hedge every summer, which will help it thicken up, until it reaches the height you want, then keep it that size.