Making yourself an admin on your Rust Server can be done the following way:
1. On the control panel click onto the file manager and browse to /server/myserver/cfg/
2. Once there, create a file called users.cfg
3. Open the file and add a new line as follows:
ownerid steamid64 playername
Replace the ownerid, steamid64 and playername with the appropriate values.
You can find your steamid64 here: http://steamid.io/
4. Click save, and restart the server.