If your university considers you a junior, then you're a junior. Some schools have a separate junior/senior quota or allow sororities to take juniors and seniors "free" (they don't count toward quota) so this could work to your advantage.
Usually, your rush application will ask you for your class year - you can put something like "Junior (graduating in 2006)".
During rush, try to mention to at least one person in each chapter that although you're a junior, you're not graduating for 3 more years - and that it's because you transferred, not because you failed a bunch of classes and had to retake them. This should get the message across that you will be an active, dues-paying member on the collegiate level for 3 years rather than just 2.
Good luck
