my big blunder at work

so i was at this new job for like 4 months and everything seemed fine until one day my boss comes up to me with a folder full of client emails that were supposed to be confidential, and says we need to discuss what happened. turns out one of the interns who was working on an important project slipped and told everyone in chat about some big changes happening soon. now i know this is something only higher-ups are supposed to know but it kind of slipped my mind. all i did was reply saying oh cool and asking if anyone knew more details, which sounds innocent enough but apparently sharing confidential info without permission is a big no-no even when its just a casual comment in chat. my boss explains that some clients were upset about the premature announcement and we lost their business because of it. i felt really bad after that because losing client accounts isn't exactly what you want to have on your record especially as someone still trying to prove themselves at work. ended up having to sign some paper saying won't happen again and hope for leniency since its my first time but yeah not sure how long this will affect me or if i'm already marked as unreliable. just feeling really guilty about the whole thing and need somewhere to vent about it.