I understand you don't want to say to much about what's gone on, but it's really hard to help you on the very limited amount of information given, both here and what was pm'd. No one can help you assess a situation if they don't know what the situation is.
There are so many variables depending on what exactly happened to who, by who, how it started, if it appears to have been pre planned, if you could reasonably have been expected to know that, and how near you were, if you were carrying/holding things for the attacker (ie coat, bag, bike) or picked anything up for them, shouted anything before, during after, what your body language says on cctv, etc. How you (and they) are dressed can say something to back up or counteract a story.
What sort of weapon was used ie length, type etc, can make a nasty situation even 'worse.' ie if someone you were out with pulls out a large knife or machete, then it's not unreasonable to assume those with them would have known they were carrying it around.
'Art and part' means aiding or abetting in making a crime happen, which can mean encouraging or assisting, which includes things like helping them look like they're part of a couple so they can get close enough to attack, or being an accessory before or at the time, which would cover things like telling the attacker the victim would be there, or holding the attackers possessions so their hands are free.
Not physically doing something ("I did not even do nothing") doesn't mean a person wasn't behind, or encouraged, or was part of an attack, or aided and abetted, or was an accessory. (I'm not saying you were - just that that's the law)
Also how old you (and possibly them) are, if you have kids, etc can make a lot of difference. I'm assuming you to be female btw.
From what else you have said your defense team would be putting forward a defense of you not knowing what was about to happen and being rooted to the spot with shock, therefore not voluntarily involved. But someone COPFS has decided their is sufficient evidence to charge you with being actively involved.
I don't know enough about Scottish law (i'm assuming because of the charges wording) to know if there is anything unusual going on here or not.
But: in the UK there would have to be something (probably caught on CCTV) that suggested you either aided, or knew what was going to happen, for the CPS to decide there was a reason to charge you with being part of it rather than a (possibly hostile) witness to it.
Given there's so little info on what actually happened to work with: why do you think you might be going to prison? Why do you think you wouldn't have a defense to the charge and wouldn't be believed? What has your solicitor said?