You installed the system's package using apt-get. That's why there is an Apache server in the system.
If you configured SSL properly, this shouldn't be the issue.
The run these commands
sudo service apache2 stop
sudo /opt/bitnami/ctlscript.sh start nginx
Did they succeed?
You can remove that Apache server in the system by running this command
sudo apt-get purge apache2
sudo apt-get autoremove