Cosmic distances are immeasurable in Earth units. Try light years: the Milky Way is around 100-180 light years across.
Out by about three orders of magnitude. I'm sure you must know this and it slipped past your mental defences. Even such a mis-estimate is a discombobulatingly large figure.
The Milky Way is around 100 to 180 kilo light-years across. Assuming the lower figure, that is approximately 10²¹ miles across. (That is, ten to the power of twenty-one. Write 10 and then another twenty zeros. Even dropping three zeros, that's still a chore.)
What a blunder. Thanks for correcting me.