My girlfriend and I had sex for the first time about a week ago. I went about 1 centimeter in, condomless and was in for about 30 seconds, then proceeded to put on a condom and go about it. What are the chances that she could be pregnant?

Let me see with the condom if used perfectly, there is a 3 percent chance since they have a failure rate of 3 percent.

If used as most people do, they have about a 10 percent failure rate,

But I assume you know condoms are far from 100 percent and there is a chance while using one.
What other birth control is the girl on?

So I would say 10 percent if you have to make a guess at a number.

No other birthcontrol. And haha yes I'm aware there's nothing perfect. She has her period the same time as her sister and her sister hasn't gotten it yet. So far I guess I'm in the clear.

Prepare to be a father, and, if you aren't, be forewarned for the future. Your current behavior, if continued, will eventually produce a baby. (And use at least three forms of birth control, please.)

She can get pregnant while having her period -- not real likely, but possible.