Did you use Reason by any chance..? The strings sound a little mechanical and could do with a little bit of reverb too. But i thought the composition was pretty good, it was very relaxing i think more instruments would compliment this piece too like maybe a piano and a double bass, but you got a good track here. Nice one
I used mixcraft to make a midi and a friend ran it through a composition program. Can't do much with it now, as the original file is long gone.
It has a pretty relaxing, soundtracky feel, but the writing is a bit overly simplistic and layered at times, what with the parts sticking to pretty much one figure the whole time and entering / re-entering successively, personally I think a bit more fluidity would've been nice.

Otherwise the actual material feels surprisingly well-written actually, it has a nice texture, although personally I would've like to have seen a contrabass and some variation in register - 1:45 or so where the middle register is given more space is nice.

The structure is a bit squarish and again I would've like it to be more fluid, but it stands relatively well as it is.

If you truly want to get into classical, I think you should take a good listen to different styles, eras and settings (orchestra, string quartet, solo piano etc) to get a decent grip on things.

And just a note, a concerto is a piece for soloist and orchestra, like this: http://www.youtube.com/watch?v=6koeS6wQHaA

If you have the time, I'd appreciate your impressions here: https://www.ultimate-guitar.com/forum/showthread.php?t=1419661
I didn't really like the way it started (it sounds forced to me at that point), but as it gets into the actual melodies, the sound is better. It does seem very repetitive though, I suggest either adding additional accent sounds (drums, cymbals, etc) or varying the main theme more as you repeat it (maybe change the chords behind it to make a different sound or invert it or something). I liked the middle, but the last few chords threw me off. It sounds like it shouldn't have ended that way... sort of half resolved, half not knowing what to do.

C4C? https://www.ultimate-guitar.com/forum/showthread.php?t=1422425

P.S. When naming classical pieces, there are a lot of specific forms you have to be cautious of to be taken seriously... I'm fairly certain this is not a true concerto. Just an fyi.