Ectopic Pregnancy?

okay ladies, so I am 4 weeks pregnant and I have been having cramps. I went to the E.R today and they did blood work, ultra sound, and pelvic exam. they said that the egg is at the end of my fallopian tube but it's still early so It might travel down to my uterus in about a week....has anyone had this happen before? it's really stressing me out