Ectopic pregnancy

So I went to the ER this morning because of some bleeding (estimated around 7 weeks). They did a ultrasound and think it’s ectopic. My hcg was at 3500 and I have to go back on Wednesday to see if it is doubling, and if not they will give me a shot of methotrexate to terminate it. Does anyone have any experience with this, and able to tell me what to expect? Obviously I’m hoping it’s going to double and everything will be fine, but I don’t know what to expect if not.