Citrus grows in spurts known as flushes. Your plants show typical growth for a plant establishing it's branching framework. To some degree there is alternation between strong upright growth as shown and lateral growth exhibited by short stems developing directly off the upright branches your plant displays.
All that's needed is for the alternating process to establish itself. Shortening the uprights will assist in keeping the plant lower. Shortening a very vigorous upright too early may induce the top bud to continue as an upright.
