So my pregnancy didnt exactly come up in teh interview... and I didnt mention it. I told the manager I was doing my corresspondence courses rather then school because I preferred to work at my own pace, and be flexible with me time, but I didnt slip in the baby.
Well I got the job, which rocks, for me. Its my first ever real paying job, and I really want to do well. But now that I have the job... Im terrified they'll fire me, once they realize Im pregnant.... can they do that?
How do I handle the situation when it comes up? How do I handle my guilt of not telling them to begin with?

Congrats girl!! :D
They CAN NOT fire you because of that and if they do you can get them in trouble.(in most states) That's discrimanation, just like if they dont hire you because your a certian race, age, height, or anything. By law they can not do that.
When I just got my job in Feburary I told my work because I know them very well and my mom works here too. They had no problem with it. I would suggest just to tell them sooner then later. If they ask why you didn't tell them at the interview, I would just suggest in a nice way telling them that it is personal and not needed in an interview because it doesn't matter about that to be hired or not..... Good Luck! :D