Calories on fitbit/video

Ok so I did a HIIT & strength workout as part of FB STRONG day 8 and another 10 min burnout workout by another youtuber but it only says I burned around 390...is this accurate or should I use the sweat on my shirt to prove that I got a good workout in?😂😂

But, how accurate are the fitbit trackers anyway? I have a charge 3