What is your user name on the tracker? Yes you should definitly seed what you leech or it is quite possible to get banned. Amounts you've downloaded and uploaded before becoming a register user will not be recorded in your account. For registered users the tracker updates your account stats each time you disconnect from a torrent. It should be noted that it is usually not wise to disconnect from the tracker by just closing your bittorrent client as there is a good chance your stats for the session will be lost. Always click your client's stop button before closing your bittorrent client.
Generally you should seed back at least as much as you download, a 1.00 ratio.
There is not an exact cut off for what ratio under 1.00 will get you banned as other factors are taken into consideration like how much you've uploaded and downloaded. If you want to be safe just assume anything under 1.00 is fair game. As a registered user you will be warned the first time your ratio gets too low and given a chance to bring it up. Make sure you check your account at least once a week as, any warning or important messages from the staff will appear under the "Your Account" section after you've logged in. A lot of people get banned because they don't check and miss warnings. As proof of this I would refer you to
http://www.datorrents.com/forums/showthread.php?t=4066
that thread wouldn't exist if wasn't a common thing.
If you have any more questions please feel free to ask.