Two things to consider here:
1. Do you get the web GUI for the router if you access the public IP from outside your network (regardless of DMZ settings etc)? Hopefully no.
2. Putting your development PC in the DMZ in order to run the webserver is unnecessary and opens up security issues. You just need to set up a port forward to port 80 in the router NAT settings.
Your more than likely can't test from within your network as the router may not support hairpin NAT. Make sure all your testing is from outside your LAN.
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