If you’re unaware that something is a sin, it is unlikely to have been a mortal sin since you weren’t committing it with full knowledge. So don’t worry about that.
When you go to confession, all your sins are forgiven: including the ones you forget to mention or the ones you didn’t realise were sins and therefore didn’t think you had to mention.
So you can relax about that.
As for your first question: well, you didn’t actually see anything profane as such. But you did place yourself, out of your curiosity, into what is called the “near occasion of sin” - i.e. a position where, by your own actions, you open yourself up to unnecessary temptation. In and of itself it’s almost certainly not a mortal sin. Venial (minor) perhaps - you’d probably have to consult your confessor to be absolutely sure, but in any case even if it was sinful, you’re covered by your subsequent confessions anyway.
Curiosity about such things can be dangerous, but in this case, provided you didn’t use what you saw for sinful purposes (i.e. deliberate dwelling on lustful thoughts, etc or acting out on them - alone or with others), you’ve probably just about ‘gotten away with it’… As I said, double check with a priest, but don’t worry too much about it. It doesn’t sound like you did anything too awful from what you describe. Just try to avoid such things in the future, to be safe.
