Should I retake the ACT or prepare for my first SAT?

Your score is actually equivalent to a 2000 on the SAT (using the chart that @Jr12317 posted above - I think he just misread the chart). There is no preference for the SAT or ACT. Practice over the summer and take the September test. (Also, some colleges will superscore the ACT so you will have two sets of scores with which to do that.)