Confused on what I owe/what I paid for

This past week I went to get my annual physical. When checking in, the lady at the front desk tells me I have a balance of $536, and she has to collect something or I cannot see the doctor. I had already taken off work and come all the way there, so I went ahead and paid the $100 she asked of me.

I put together that it was most likely for my xray I had gotten a few weeks prior. Different location and doctor, but same healthcare provider. However, at this point in time I had received no bill or EOB about it. Until that point I didn’t know if I even owed anything and what insurance had covered.

The EOB i just received says it was over $1k total and I indeed owe $536 after insurance. I still haven’t received an actual bill for the services yet, but I can see my balance online and it says I do owe $436 more which makes sense. It’s also not due for another month.

Should I have pressed more on what I was paying for at the time? Even though I connected the dots and knew it was probably the xray, she was unable to tell me what the balance was for. I get it’s standard practice to try to collect money so I can continue to use their services, but I’m unsure about the whole situation and it made me a little uncomfortable not being able to know what exactly was going on.

Should I ask for an itemized bill from the hospital? More than anything I’d just like to see what services I was billed for to make sure it’s correct and how to pay it. Haven’t had much luck thus far with getting info from them