I'm 5'2 @ 120-125lbs, what fitness plan at the gym would be best to get a toned butt, chest, and abs?

Full-body Workouts. At the gym you're pretty much "on your own" and will need to construct a personalized fitness program. Consistent full-body resistance training alternating with aerobic activities will be optimal. Many gyms offer a variety of fitness classes; if they're aerobic-based you'll need to supplement with resistance work. Toned abs require special attention to diet and calorie consumption.
PREs. Progressive resistance exercises-weight training, pushups, abdominal crunches or situps and stair climbing.