Possible ectopic questions- worried about methotrexate, etc

After an up and down roller coaster of my low hcg dropping and rising then dropping again (now at a 78) and I am supposed to he 5-6 weeks pregnant), my Dr is worried it's an ectopic or pregnancy in unknown location. He told me to come in tomorrow for a check up then he will send me to the hospital to get a single methotrexate injection to terminate the pregnancy wherever it is to avoid a tube rupturing.

When i asked him if he could diagnose an ectopic for sure by ultrasound he said no it's too small won't see it, although i want an ultrasound to confirm it's not in my uterus so i can just pass it normally without the drugs? Is it normal for them not to do an ultrasound before methotrexate because the pregnancy is too small? I expressed i'm worried about taking the methotrexate as it's a chemo drug and I rather not ig i don't have to (I know the pregnancy isn't viable from the up and down and dropping but I was hoping for another alternative to that gnarly drug). I'm told we have to wait months to conceive again and also the side effects can be painful and bad. i'm mostly concerned about that drug in my body.

Would you accept the shot without an ultrasound?

Any advice greatly appreciated.