If you want to major in music performance in guitar, I'd say give it a try. If you have two years of practice playing then you must be very familiar with technique and somewhat exposed to theory. Therefore, by having at least that, you and your instructor could dedicate the most part of the lessons to theory and music composition, its incredible what a person can learn in a year...
As far as the audition, well if you take theory lessons about scales, chords, etz. then you will be familiar with song composition and the different styles of music, so it will be a little less hastle than you might think.
In my opinion I would really think it over, specially with your parents ( I am assuming they might guide you a bit on your future ) and with music instructors. At least my way of thinking is that opportunities come as they come, if you have nothing to loose by auditioning, then go on and try it, you never know!
anyways, luck with whatever you decide...