Newly planted crepe myrtle roots exposed
Those roots should not be exposed. Get some top soil and cover the roots. You may want to create a saucer by building a 2"rim about 1 foot out all around the base. This will hold water longer close to the plant, so the water has time to soak in and not run off. The rim will naturally level off as the plant ages.
Be careful to not heap soil high up the trunks. Make the soil level the same as it was in the pot.