With all of today’s technology, you would think there would be a 100%-guaranteed-to-never-streak-ever-self-tanner. I really do not think there is, and that is ok because when your tan starts to streak, turn to something more low-tech and simple: lemon juice and baking soda.
Mix fresh squeezed lemon juice (its natural acidity gently bleaches away unwanted color) with a few teaspoons of baking soda (a fabulous natural exfoliant) to make a paste. Use it next time you shower, and all your fake tan woes with disappear along with the streaks!