Then if its still leaking, there is still a problem

First of all is the ring the correct size for the fittings you are putting it on? Including the hose? And is the hose end in good nick? If your unsure cut a couple of inches off the end of the hose and try again.
If you feel the fittings are the correct size, then try adding some ptfe Tape underneath the ring and then try again.
I use a pair of tack removers (pinchers) to close mine with and never had a problem
Failing all of the above and to save you any further embarrassment when entering the bank, I have been kind enough to provide you with a link for you to purchase some colostomy bags
http://www.cancerhelp.org.uk/help/default.asp?page=3780