A new WeabAPI by VALVe can help to get answer to your question "Is my server listed on the master server?". Here is an example:
Just replace "SERVER IP HERE" with your server ip. If you don't specify server port then API gives you list of all servers registered from this ip on master server. Most importantly, if you see a "reject" field, the status code indicates why your server was rejected.
My script to check your server in valve master-server: /smaster/steam_ms_listing.php
This API works only VALVe master-server. If you want to check your server in other master servers you should check out HL Master service.