is it safe to use this bottle still??

i found a very old bottle in the diaper bag from like a month ago. it was filled with formula milk. i dumped the milk out and rinsed it. Then i boiled the bottle and then steamed it in the sterilizer in the microwave. Is it safe for me to use for my two month old now or is it better just to throw it away because of how long the milk was in there?