An i-9 is just a government required employment verification form. See: http://www.uscis.gov/sites/default/files/files/form/i-9.pdf
It is not a contract with an employer. Go apply for other jobs.
You should not fill out an I-9 until after you accept the job offer. However even after you accept the job and begin work you will not be restricted from applying or getting offers from other companies. Good Luck.