Your calculation is a little confusing.

Could you add '(' and ')' around the multiplication, so it is clear that the multiplication is done first.

To solve your problem, go back one step.

Show the value of analogRead() on the serial monitor without the average.

I assume the heater is powered by the mains ? 110 or 240V AC ?

If so, you will read AC values, changing at 50Hz or 60Hz.

The average of a AC value will be zero.

You have to know what the numbers ".0264" and "-13.51" do, and explain that in the sketch. You can't write a good sketch if you don't know what those numbers are.

By the way, I have no idea what those numbers are, I would calculate the voltage of the analog input and use the sensitivity of the sensor in the sketch to calculate the current.