|I bought a dynamite crape myrtle - :whit II|
|Crape myrtle 'Dynamite' has a shrubby growth habit rather than an upright or tree form. It was introduced in 2006 as one of only two true red flowering crape myrtles and is attributed to Dr. Carl Whitcomb (which is why the plant tag includes "whit II').
It typically grows 10-15 feet tall and 8-10 feet wide and when grouped together can be used as a hedge. You can prune it back to keep it in shape (and in your case under control). Crape myrtles produce flowers on new growth so if you prune it back in early spring it should be covered with flowers in early summer. If you prune it back again after the flowers fade it should produce a second flush of flowers later in the summer. By all means prune back the errant branches to train it into the shape that you want.
Best wishes with your garden!