You probably bent, twisted something or possibly pulled out a few clips that hold on the body panels. Or like mentioned above lost a weight on your rim and now your tire is out of balance.
Not giving any parenting, as you did it on a closed course in a safe environment, and its your car. But this is a good example out there for others, that these cars are not aerodynamically sound to travel at those kind of speeds.
2014 Mustang GT Base MT82 -Stock 3.73s, Roush axleback, Steeda 93R tune, Steeda Hi-flow X-pipe, 19" Charcoal AMR's, smoked front and rear side markers, 20% tint, quarter window louvers, Steeda Ultralite springs, Koni Str.t shocks/struts, MM camber plates, J&M adjustable panhard bar, BMR LCAs and relo brackets, Barton shifter and 2-post bracket, Black Modern Billet Grilles