welcome to the forum @Mcinc 
you didn’t tell us anything about your DNS. given the config you provided I would expect you can reach your NC on docker_host_ip:9321 (btw very bad choice - I recommend 80 or even better reverse proxy and 443) most likely this is not what you are looking for and you want to create a DNS name, which you in turn configure in the pihole and point to your docker_host_ip but start with easy steps…
Please use the required support template - there is a reason why this exists… and use the search function - chances are high simple questions like yours have been discussed in the past…