My thumb will lock up next to my index finger a lot. and just now my index finger was locked spread away from my middle finger quite far. what's wrong?

Muscle spasm: The symptoms you describe are from spasm (prolonged muscle contraction) of the small muscles of the thumb/index finger. This can be caused by a variety of conditions, but most commonly fatigue of the muscles from overuse, dehydration, and/or new activities that tax these muscles more than usual. At your age, it is unlikely a serious concern. If symptoms persist, recommend a virtual consult