Your initial assumption is in error: your tub can easily climb to the mid-nineties without the heater being on at all. The little circulating pump can do it all by itself, assuming the tub has a good cover tightly fitted.
You have a reset button on that heater (unless it has been updated) and I would start with that. However, it WILL NOT reset if the heater is above 90 degrees. Simply shut off the power and wait several hours. Leave the spa cover closed: no sense it cooling the entire tub, just the heater.
HTH