Someone who knows about money (as in how it's handled in certain situations) please read and answer:)?

Right, A few months back we paid the first half of the money needed for me to go on an oversea school trip which takes place in February, but now I realise I actually can't make it!! Ooops! I plan to go and speak to my teacher in the next few days about pulling out but I'm a little concerned about whether I'll get that money back...will it have been sent off for the travel arrangments? And even if it has what are my chances of getting it back? Thankyou in Advance x