Hi Girls try not to worry too much about cysts of that size - I too had one that was 4cm - they scanned again about 8 weeks later, and it had totally disappeared. The gynae did say that it would not have caused any probs conceiving though, so try not to get too worked up about it.
Cysts come and go with your cycles, and most of them will go on their own.
HTH
Maz xxx