Hey MrZhume, congrats on the lucid.

It could be either, but I'm going to put my bet on lack of control. When you want to fly (or do essentially anything else in a lucid), you have to imagine and picture how you're going to fly. If you just say, "I'm going to fly now" without doing anything else, the dream will render its own version of what 'flying' is, whether it be floating or something else. You have to help the dream out by visualizing your method of flying, and knowing 100% that you'll be able to do it. Also, don't think of flying as a chore or get worked up about it; just do it without a second thought. If you look and feel like you've done this a hundred times before and will be able to fly with no problem, it'll help a lot.

Good luck.~