Any time you have unprotected sex and the guy comes in you, the possibility of you being pregnant is there. Even if the guy hadnt fully come in you(say he pulled out) there is still precum. Even just a small droplet of precum contains like over 1million of his "little soldiers". Just because you didnt get pregnant the first time doesnt mean that it wont happen. Im sure you realize this and it probably sounds cliche but to some girls it doesnt really click until they get pregnant. So, to answer your question, yes, there is a possibility.

Honestly, if you dont want to get pregnant or you dont want to get caught please, use some form of protection or just stop having sex altogether. Protection doesnt always work, I know, but atleast you tried to prevent it. And if you do choose continue to have unprotected sex, just know the consequences and the possibilities.

How big a chance is there that I am? Is it slim?

Oh, also, i'd have symptoms if I were pregnant, right?

I honestly dont know how narrow of a chance it is, every girls body is different. But I know the possibility is there. Me and my bf had unprotected sex for 4 years and I didnt get pregnant till this year, our 5th year together. I dont think you would be getting symptoms this early though. Its really to early to tell. Unless your period is late and you start to experience pregnancy like symptoms then its really hard to tell.

every pregnancy is different.....You have many symptoms or you could have none