apart from when using the gym.. so you have a membership? what do you do at the gym.
Basicly, the body is a complex thing. if you work only your biceps, they wont get big without working other parts of the body aswell. Exercises like squats and deadlifts put alot of preassure on the body, which causes the body to send out hormones that will not only make your legs and back (which squats and deads mostly work) grow, but your entire body!
Also, one argument is that your arms will only be as large as the back will let them. The biceps are really "made" to assist in heavy pulling movements like bendt over rows (google exercise names if you dont know them, to get an idea) so if you got a weak upper back, it makes no sence for the body to get strong big biceps

Also, some say your arms will be as big as they need to be, so when you can bench, row, chin and military press high ammounts of weight, your arms will be bigger, because they need to be.
Search "full body workout" on this site, and it should give you some ideas of what to do with 3 days in the gym working the entire body (which is probobly what you need)