Two days a week is fine for the beginner I think. Our Senseis recommend no less than two days for training, however. If you're going to train for two days a week, stick to it. Be disciplined, and show up on time, ready and properly outfitted.
In any case, you'll eventually want to train more and more. My personal experience was similar: I started off 2 days a week, then 3, then four, etc. Now I train six days a week; 1 1/2 hrs Monday-Friday and 2 hrs on Saturday. Although I've had to cut back a little due to work I try to make it at least 4 days a week: 3 days M-F and definitely Saturday.
My girlfriend says that when I don't go to every single class, I get all cranky, though. I certainly feel anxious and I get the jitters, like having an itch I can't scratch, or something. I get irritable and impatient too. But I feel much better as soon as sit ins seiza for a while, do some ukemi and Ikkyo someone. Please tell me this is normal, please, someone? It's normal, right? Please tell me, I'm not an... Aiki-holic!???