Walking in Place to Burn Major Calories

So i tried walking in place at home because im pregnant and its really hot outside and i have 2 kids, 6 and 4, who wont last very long in this texas heat while i try to go for an actual walk lol. I constantly checked my HR to input it in a calorie burn calculator when i finished. My HR ranged from 114 to 129 for 45 mins. When i calculated based on my height (66 inches) pregnancy weight (165 lbs) age (28 yrs) Gender (female) fitness level (good) i got a NET calorie burn of 252 using an avg hr of 119. Does this sound accurate? I was walking, while punching or doing other arm movements, and at times used 3 lb weights in each hand.