English Translation
I’m in the other ambulance!
“The other” is not translated in Japanese. It should be:
私は別の（べつの）救急車の中にいます！ or
私は別の救急車にいます！ – Omitting ～の中 sounds more concise and natural.
私はもう一方の（いっぽうの）救急車にいます！-- もう一方の precisely captures the meaning of “the other”. 別の merely means “different”, and doesn’t compare two things and pick up the one.