In terms of processing the information and data, you certainly broke the rules.
Even assuming it could have been easier for you to work on your machine, you should have asked the authorisation to do that.
Unfortunately, this happened and what you will have to do, once you receive a formal communication, is to clarify/explain that you did it with no intention to break the confidentiality of the data.
However, my advice is that you speak with an employment solicitor so that, if necessary, you have a "defence" ready.
You may also open a new question here when you hear from the HR, but this kind of situations must be assessed by a solicitor also examining the papers.
I hope this information is helpful and I wish you the best.
Please do not hesitate to contact JA again if you need help and you may ask to speak with me directly if you wish.
Regards.