calorie burn estimate

hi everyone,

i just did a class at my gym that is a direct knock off of les mils body pump. my smart watch ($20 kind not apple or samsung) said i burned 90 calories the whole 70 minute class. the watch also says my heart rate averaged 104 during the class compared to my resting of 75. it was a long class and i did have to mod the moves bc im just getting back into working out. im 28f, 290lbs. my fitness pal says i burned 700 which seems high. other online calculators said about 450ish. what do you guys think? im still going to eat my normal diet of 1200-1800 cal and 100g protein.