littlepom,
At the end of the day you cant go back and change things... you tried it and you told the RAF you did. Guarenteed something like that WILL have gone down on your file.
Stick to your story and if it comes up at OASC (which it probably will) then answer something along the lines of
"I did sample cannabis when i was at university but found that i did not like it and have not touched it since. I understand that drugs and service life do not mix and would never dabble in it again as it would be a risk to both myself and others."
Make it clear you understand the RAF's policy on drugs, but also don't go back on what you've said. As pointed out, OASC will respect you for being honest and sticking to your story, but you have to make it 100% clear to them that you understand its wrong and that you wouldnt do it again.
Best of luck
