jagsfan05 you are needlessly worrying. I know Ive been their and done that.
I read a thread where you were afraid that if you only hit your biceps once a week they would atrophie. Will I hate to dissapoint you but they are not going to shrink.
Remember when you do bent rows or pulldowns for your back your are also working your biceps. When you do Bench Presses or any presses you are also working your triceps. Think about it,your arms have to be grabbing and either pulling or pushing against something eveytime you train your upper body. Pushing spells tricep involvement pulling means bicep involement. If you are directly training your triceps are biceps twice a week I hate to say it but you will not get those biceps your desiring. If you hit those larger muscles super hard the arms will take care of themselves. I get a kick out of folks that tell me they need to train each muscle group twice a week. The body doesnt know and doesnt give two shits about what day of the week its is being trained. All it knows is how the weights are tearing it down and how it needs to recover and adapt to what your throwing at it. The human body has to be subjected to something it has to adapt to. Just like 0311 wrote
Rome was not built in a day"
I also think that as thin as you are you need to make a descision do I want to gain mass or do I want to keep playing tennis and weight training and spin my wheels the ball is in your court.
Good Luck