Should be 116 burn damage.
Damage is based on your attack stat - this doesn’t look like a fully-leveled hero.
Max special skill lvl 8.
Not just skill level - the actual Attack stat of the hero. Yours is 607 attack right now - the burn damage will increase as that goes up with leveling the actual hero.
Read more here: Jean Francois - DoT not at 304? - #2 by KLinMayhem