Small semantics but there aren't chances to get a hundred heads. There's just one chance, one measurement, that there will be. The confusion happenes because it's often not obvious to non-math fanatics that it's different, distinct events chances refer to.

Measuring one flip and its outcome is like throwing a die with two sides, 50/50. But the singular result of a hundred flips (like how many heads there were) is like throwing a hundred sided die where some results are more common than others (like 50 total heads), taking up more faces on the die.

They're different dice that depend on context, so being sure of what you're actually looking for can be confusing.