The way I see it......... extra != confinement.....
I see extra as extra weekend duties..... You have to do the duty
instead of someone else. So while you're being punished, in a way,
you're also doing something good for someone else. Someone else
gets to go out with his girlfriend and enjoy the weekend instead of
you. Not much of a consolation for you, but you can take heart in
knowing that someone else benefits. 
Confinement, on the other hand, affects only yourself. Someone
still has to the the weekend guard duty.
Signing extras for pretty trivial reasons are pretty common in the
SAF. Heck, I once got two extras for not polishing my boots during
stand-by bed. I was so concerned about cleaning my bunk that I
forgot all about my boots. 
My advice to you..... Just take it like a man and accept it.
