Help me school probz?

I was in school the otherday minding my own buisness and my friend was hangin with me and this kid came up to me and pushed my mate around so my mate picked up an orange and threw it and the juice landed on his '�45.00' shirt ( this kid lies and snitches a lot ) and i went to pick up the orange and i walked past the other boy i was messing ad threw it over his shoulder and an other boy hit him with an orange... Today we were on a trip and i went home early and later my mate rang me saying the head teacher was making me and him pay �22.50 to the kid who was bombarded with oranges but the other boy who threw the orange said i hit the kid with the orange and my friend i had to see the head teacher tomorrow and my mate said if i tell the truth i can go on the trip tomorrow and if i lie i dont get to go on it... I need advice