Kelley Marie Ferguson, of Laguna Hills, Calif., could have faced up to 20 years and a fine of up to $250,000 for planting the notes aboard the Royal Caribbean's Legend of the Seas.
Ferguson, 20, who hid that she was pregnant during the April cruise, told authorities she wanted to cut short a family vacation to return home to her boyfriend. The ship was diverted to Honolulu after the notes were found.
"It was done without malice or intended to hurt anyone," her attorney, Loretta Faymonville, told the judge. "She was pregnant. She was scared. She wanted to go home."
Ferguson had a baby girl June 25.
She'll begin serving her sentence Nov. 4.
U.S. District Court Judge Helen Gillmor also ordered Ferguson to serve three years of supervised release, and to undergo a psychiatric evaluation and counseling, if needed.