I'm so, so sorry you're going through this. I'm really not qualified to give you any definitive answers, but I will gladly share with you what I did & thought, as I went through something similar with a happy ending.
Below I have pasted in my timeline, which you can consider, for what it's worth.
I went for many an early u/s & like you mentioned, with low betas, it's unlikely they will see anything. They were looking for anything unusual that would suggest an ectopic. Nothing was seen until very late, as you can see from below.
I can't say if you should hold out any hope. Since I had a live birth out of my strange scenario, I will always lean toward "anything is possible." Certainly situations like mine & yours usually do not end well, but who's to say where the line between sometimes & never lies?
I did not agree to do a methotrexate injection when my RE suggested it. I was about 6 wks. along at that point. The other doctor I had gone to see for an u/s thought he saw a sac in the uterus but couldn't be sure. He said no to the methotrexate, that we needed to wait a week & verify. A week later, a uterine sac was confirmed & there was a heartbeat.
So for me, I would not agree to it in the absence of confirmation of an ectopic pg. I felt, based on what the doctors could tell me & my own independent digging, that my health was not in danger that early on so there was no harm in waiting it out. If they are able to confirm an ectopic, that is different, of course.
This is a fairly unusual situation & it's even more unusual to report a healthy pg. & live birth, as I had. Still, I'm not completely alone. There have been other "miracle" pg. stories. But the women in this situation who end up having a m/c or an ectopic certainly outnumber the women with miracle pg. stories.
I would just suggest educating yourself so you can question your doctors & make the best decisions for yourself. Clinics certainly do have an eye on liability so that factors in. I was given no chance of it working out by my doctors, based on my betas, & I certainly didn't believe it would, but I felt I had to ride it out & wow did that prove to be a good move. In my case, the answers I was getting to my questions weren't really making a lot of sense, so that made some of my decisions, such as to keep riding it out, easier.
I hope things do work out & I'm so sorry you're going through this. I still remember what a terrible, terrible time it was for me.
Here is my beta pattern - dpo followed by beta #. It was a FET with 2 blasts.
11 dpo 26
13 dpo 53
16 dpo 39
18 dpo 41
20 dpo 72
23 dpo 179
27 dpo 559
30 dpo 921
31 dpo - "possible" sac seen in uterus - ob through RI's office said it doesn't look good, but he wanted to wait another week & felt it was too early to consider methotrexate, which my RE wanted me to do by this point
33 dpo 2671
37 dpo (7w2d) - last beta drawn at 4238 - ob through RI's office saw a sac with strong heart beat, but said it was misshapen & likely not viable - told me to come back in a week
40dpo (7w5d) - u/s with local peri. - measuring 6w6d - heart beat strong - sac looked fine - everything looked fine - I canceled my out of town appt. with the RI's office - it was quite a while before I actually believed the pg. was normal, but I had a healthy baby at 37 wks.