Kate,
I'm really sorry that you're dealing with this; I know from personal experience just how incredibly difficult it can be when things come up that you're not sure happened, and/or that you wish had never occurred. I too have memories that I'm not certain about (sexual abuse related as well), and I know how intrusive and difficult to manage they can be, and what an intense impact they can have. My best advice to you would be to practice an awful lot of self-compassion, and rather than focus on the content of the memories (which can be really dysregulating), pay attention to and do your best to deal with all the feelings that come up. Regardless of what exactly did or didn't happen, the feelings you're experiencing are very much real and deserve respect and the proper attention. Please take good care of yourself, and know that there are others out there who understand.