BFP at 41 —Beta numbers concerning ?

My husband had been trying to conceive since we got married 3 years ago. We have had 6 failed IUI’s and have also tried on our own. We were just going to do our last little bit of paperwork to go to an actual fertility clinic that does IVF. But unbeknownst to me, the day before our 3rd wedding anniversary (my period was due on our anniversary) I didn’t want us to be heartbroken on our anniversary so I took a test the morning before just to get it out of the way and it was POSITIVE. We have never gotten a positive before so I just can’t believe it. Anyway, I called my local fertility specialist that did our IUIs and told them I got a positive pregnancy test so they had me come in that day (the day before my period was even due) to do a beta quantitative blood test . That day it was 86. Then two days later it was 141. Of course it had not doubled but they said 60% increase is within limits. They weren’t going to do another beta, just scheduled early ultrasound at about 7 weeks. Of course I called and asked doctor if she felt worried about the results and she wasn’t in that day so a different APRN said we could do one Monday (4 days later) and I agreed. That was today and it was 390 (this is at 4 weeks and 5 days) and within the 65%...The nurse that called said we are “cautiously optimistic” which made me feel like it was not a good sign. Has anyone had these types of levels and still carried the pregnancy to term? I’m so worried now!!! Please help me understand.