Bring nothing for them, admit nothing. Consult a lawyer for a few hundred to get advice.

Depending on the size of the company and severity of the information in question, you just need to say very noncommital and very specific phrases (lawyer speak):

I understand your concerns, however I think there has been a misunderstanding. How can I help resolve your concerns?

Again consult a lawyer. And tread the fine line between being contrite and admitting anything. Even in my advice I almost worded it wrong. See a lawyer. You admit nothing concrete because your admissions become fact, give them nothing without a lawyer, because even if you truly did give them the only PC and USB stick with it on it, acknowledge nothing directly (again this becomes admission in a legal sense). Whatever evidence they have right now, it is on them to prove intent unless you do it for them. And they don't want to spend on legal fees for no reason.

In the end you want them to have the feeling that this was truly a misunderstanding while giving no admissions to concrete actions like copying, moving, or replicating any data. They may have records, but that's a different matter.

It may be that a lawyer could just act as an intermediary to clarify, and ask what evidence they might need to feel assured in the safety of their IP. Note: most documents produced while at an employer are technically company IP in most cases, and you aren't alone wanting to reference your own code work, but many companies are paranoid about this for good reason.

Try not to lose your nerve. You just need to plant your feet, and keep in mind you have done nothing wrong morally. You have fucked up technically, but your mission now is to keep their trust in your somehow without digging your hole any deeper. So again, speak with a lawyer and get the right language.

The company does not want to waste money suing you. So don't hand them an obvious violation that have to pursue. Try to keep it together. Remember your intent. And convey that, as obliquely and in indirect statements as you can.

I don't want any issues with XXXX corp, and always planned to have a good reference from my time here. The files XXX Corp is concerned with today hold no value to me, only my personal photos and data do. If you could acknowledge there's been no wrongdoing I think we can easily resolve all this.

Avoid the temptation to let them set the terms too much. They will ask for devices and hardware. What you want is a document clearing you of any wrongdoing before you provide anything that could be used against you. Then handing things over might be okay. Again. Speak to a lawyer, even briefly.