No, marriage alone does not give you automatic U.S. citizenship, you must go through a legal process to apply for it.

You must apply for a green card first, Marriage to a U.S. citizen allows you to apply for lawful permanent residency (a green card).

The correct process is a K-1 fiancé visa if you’re outside the U.S. This visa lets you enter the U.S. legally to marry your U.S. citizen fiancé within 90 days.