too many onion sets

I appear to over ordered my spring planting onions and was wondering if i can store them in a air tight container til next spring?

I don't think that would work.  Any time I have tried to keep onion sets for too long, whatever the conditions, they have ended up mouldy.  A better idea may be to join or start a seed exchange scheme, (it only needs two or three people), and exchange the surplus sets for something you need but haven't bought yet.