Jcerillo, I'd swing by an archery pro shop sometime soon, and take your bow with you (and I'd bring an arrow too). They'll be able to check your string for you, check your draw weight, ensure your draw length is correctly set, etc.
They should also be able to help you pick the right arrows (as far as length and width) based on your draw length, draw weight, etc.
I just got a Bear bow about six weeks ago. I'm shooting at 70 lbs, with a 29" draw. The guy who sold me the bow and set it up cut my arrows to the proper length, and told me that based on my draw weight and length, I should be using 300-width arrows. He was super helpful and full of information in general. I'd try and find someone like that. Shouldn't be too difficult.
Edit: BTW, what does that 300/400 number represent? Is it "0.300" and "0.400", as in, "3/10" or "2/5" of an inch?