Your question is headed “Affray”, but you have not said whether you have been charged with affray or not. Just because the incident involved a number of people it does not necessarily constitute an affray. This is a specific Public Order offence covered by Section 3 of the Public Order Act. It is a serious offence and carries a maximum of three years custody. It is also unlikely that the CPS (who has to authorise the charge) would have done so in such a short space of time since the incident, especially at the Christmas period.
There are a number of other offences you could have been charged with. If you are charged with affray all the circumstances of the incident will be considered, but this extract from Magistrates’ sentencing guidelines may help:
“Fight involving a weapon/throwing objects, or conduct causing risk of serious injury” – Starting point is 18 weeks custody.
At age 17 you would normally be dealt with in the Youth Court (where the potential sentences for offences such as this are less severe) though you may appear in the adult court if you are charged jointly with the others (those over 18) for offences arising from the same incident.