Good thinking! We know that water gets converted to water vapour all the time. The water's temperature is definitely not as high as $$100^{\circ} \, \mathrm{C}$$!
It is true that if you heat water to $$100^{\circ} \mathrm{C}$$, all the water definitely gets converted to steam. But, even if the temperature is not that high, some random molecules in the water can still escape the force of attraction of the other molecules. This is called Evaporation.
Evaporation is very different from boiling (vaporisation) because evaporation occurs at all temperatures above $$0^{\circ} \mathrm{C}$$, not just at $$100^{\circ} \mathrm{C}$$