Shell script to get public ip from VPN docker container

trying to create a shell script to schedule and run. But with what i have it keeps putting the local ip of the box in my txt file and leaving me at the bash prompt in my console. (commands work perfectly outside of the shell script so i know what the ip should be). here is what i have, thoughts?

docker exec -it vpn /bin/bash

curl icanhazip.com >>vpn_publicip.txt

exit

also new to this so sorry if im way off.

thank you in advance.