[Debaser]

Yes, there is a chance that the baby is yours. The only way you can find out for sure would be to do a paternity test after it's born.
You may have pulled out before ejaculation, but that's not a reliable form of contraception and there is always precum. So the chances may be slim, but there's still a chance.

You redeem yourself slightly by encouraging her to get some emergency contraception, but by the sound of her reaction (irritation at your nagging) i'm not certain that she did. She may have, by all means, but if it was me in her situation, i'd be dragging you down to the clinic too, worried out of my mind.

On the other hand, she could have taken the pill, slept with someone else and got pregnant, nothing to do with you at all.

The first step you need to take is TALK to her, just plain out ask her. And i'd hope she'd be honest with you. How many weeks is the scan? Do the dates match up to your sexual encounter?

Get the facts together and then go from there.
Also i have to add, unplanned parenthood does not ruin your life, nor your chances of future relationship it just means a lot of responsibility at an early age.