SSL VPN Public IP

I'm new to firewalls so keep that in mind if I seem like i don't know what I'm doing. 

I'm setting up a SSL VPN for my company and I can't connect to my public ip. Whenever I try, i get a timeout. When I'm inside the internal network I can connect to the local IP and get to the user portal. When i download and install the VPN exe from there and go to a different network, I get this message: "TCP: connect to [AF_INET]PUBLIC IP:443 failed, will try again in 5 seconds 
Fri Feb 09 10:46:13 2018 MANAGEMENT: >STATE:1518169573,TCP_CONNECT,,,,,,

I don't know where the mistake is since like I said this is the first time I set up a VPN via Sophos, maybe someone knows what kind of mistake I did.

Thanks for your help