PLEASE HELP ME. NOT SURE IF PREGNANT

I'm on my 27day of my cycle. I usually have a cycle of around 36 days. I had sex on the 13 day of my cycle. We used a condom but it kinda got stuck inside of me and when he noticed it didn't feel right he withdrew before he came and the condom fell off a little and after he withdrew it was way inside of me. I did not use plan b and was only at a 3% chance day. However I had been feeling very naseua lately and I had a red spotting two days ago and a brown spotting yesterday. I am very nervous but in the past I have felt mad use because I always freak myself out about it and then stress out. Also the days I had spotting were the twoost stressful days I have ever had in my life so I think it may be from that but I'm still so scared and don't know what to do. Please help.