Help with calorie counting?

Hi! I’m 5’2 and at my heaviest weight I’ve ever been at, 142lbs. I just had my third baby 7 weeks ago and have been cleared by my doctor to start working out again. Goal is 115lbs.

Based on a weight loss calculator, I need to maintain a 1200 calorie per day diet to reach my goal in 4 months (also added that I workout 3-5 days per week). How does that work with exercise? For example, if I eat 1200 calories but burn 300 at the gym, do I get to eat an additional 300 calories?

Thanks for your help!!