So how can I make it look like I'm actually playing the rugby game, but instead I just want to be running around near the back of the pitch, not getting involved in the contact.

Just stand back and fallow the ball without being close enough to actually have to take part. Run at full speed and look like you are interested, shout good things to your team mates when they have the ball

I cant believe that you are forced to play rugby

I don't believe for a second you are being forced to play full contact rugby if you don't want to. Health and safety would over your school like a rash. Nevertheless play at scrum half, so all you'll have to do is: pass, kick and shout, shout, and shout some more to forwards. just pass the ball away and you can go the whole game without being tackled or tackle anyone else playing at scrum half, if so wish to.

man up

Hey friend unlike you I love to play rugby! iv played it for about 2 years now if you dont want to play it stand about 5 meters back from your team and side step in a line where the ball is and if your teacher asks say im playing fullback (just say fallback) I play that position but unlike you i love to get contact xD

Contact sport should not be compulsory at school if you get injured will the school pay compensation (money for your injuries)?? tell your parents about it.