What happen if i shoot to a foe that is in melee with an allie? I have -20 BS and all the bonus for range, full auto and so on?

What happen if i'm shooting into melee and i go out more than 3 degrees?

Thank you

Pray His name

Nothing, it is just a miss. You can only hit allies/wrong target if the GM chooses to exercise optional/house rules.

Which means you should check with your particular GM, as the optional rules can be harsh (allocating hits to allies for autofire, etc).