Don't worry about it dude; you already put on 4 lbs so who cares if you took 1/2 a scoop instead of a whole one. You didn't waste your time, bodybuilding is a marathon, not a sprint. You have a whole lifetime to get big. Up it to 1 full scoop this week followed by a full sering next week.
Check out these threads if you haven't already. Their authors know their sh*t. Now start getting big! :bb3:
The "No Frills" Bulking FAQ
Another "How To" Bulk Thread
Gaining mass in a nutshell (a big nutshell)