AJ (and as you've realised yourself) is absolutely right - you really should have declared the conviction.
In any case, you haven't helped your situation at all. The fact that it was so recent, is for theft, and if the CO chooses to take a hard line they may consider your statement that there are no convictions to be a pattern of dishonesty.
All is not necessarily lost, however - this is all pretty much guesswork. The single most important thing to do is contact your CO and discuss the issue. As AJ says, you're going to have some explaining to do, but migration is a very stressful activity and you won't be the first applicant to have made a mistake in the heat of the moment.
Contact your CO, be absolutely 100% frank, open, and honest - I can't stress that enough - and see where that gets you. You've come this far so giving up isn't really an option.
