If you cast it so that it’s point of origin is 150ft away from you, then it would expand both 93ft towards you and 93ft away from you. By expanding 93ft towards you, there’d still be a gap of 57ft between you and the edge of the fireball. The farthest point edge of the fireball would be 243ft away.

So Fireball makes a 20ft radius sphere. That’s a sphere with a volume of 33,510.322 ft^3 A sphere 100 times bigger would be 3,351,032.2 ft^3 Such a sphere would have a radius of 92.832ft The range of fireball is 150ft, so you could safely cast it’s 100x magnitude counterpart. Of course this is a very simplified idea of what 100x magnitude fireball could do. For instance, does it do 100x the fire damage? ~2,800? That’s over 50.9x more than lava (which is ~55). Does that mean it’s 50.9x hotter than lava? Making it 35,630-61,080 C, 6-11x hotter than the surface of the sun? These calculations are all fast and loose as actual explosion calculations are too complicated for my little brain.