I'm no specialist, but I'm quite sure that if you really want to learn a Nocturne you will be able to do it, many of them are not extremely hard, and I still find them very beautiful pieces of Chopin music...
I did manage to learn Opus 9 No 2, it still need some work on some parts, and I've been playing for a few time.... Opus 9 no 1 is also really nice, but is harder.
You could also give a listen to some of his Waltz, he wrote many great ones, both of the opus 69 are quite beautiful, and not very hard.
Give them a listen, choose one you like, and take a look at the sheet, I think the most important thing is playing things that you enjoy, take some pieces and talk to your teachers about you playing them.
I've been learning Mozart's Rondo Ala Turca, this is well known even for people that don't listen to classical, and if I've been managing to pull it off you can certainly do as well.