Some Previous Employment Can't be Verified- am I fucked?

Hi, I'm currently have a IB SA 2022 offer, and have started the whole routine background check procedure. The issue is that I did a couple of unpaid internships, and, though I did mark them as unpaid on the form, as a result I don't have any form of W2 or paystubs to verify employment. I did send in my offer letters as documentation, however that wasn't accepted. One of my references also has not responded to the background check people despite me emailing them ahead of time and getting their consent to put their contact as a reference. I'm really stressed about this whole situation- am I fucked? Will my offer get withdrawn because half of my employment history can't be verified? What can I do in a situation like this?