Morning after pill

My fiance and I had sex and we use the withdraw method. We already have @ 1 year old daughter. So anyway he pulled out yo late and came inside me. The next day I took the morning after pill but I was told that it may not work because if you weigh more then 165 it stops working. I weigh about 206. I was told to come back Tuesday for the copper IUD. Back in sept I was on the depo. Unsure if its still in my system. But what should I do? I can't have another baby now!!!