- First, communal absolution is only allowed in extreme cases. For
example, a bunch of soldiers are about to storm a beachhead and there is no time to
hear everyone's individual Confession. Nevertheless, your Confession was valid although illicit.
- Second, after receiving communal absolution one needs to go to individual
Confession after the crisis is over, if one survives.
- Third, if you've been to Confession since then, you've been absolved of
all sins prior to that Confession regardless of whether or not you remembered
to confess them.
That said, it doesn't sound like
your intent was to do something wrong. God looks at the heart.
For starters you came back to Church, so your
heart is in the right place.
I would mention it in your next Confession. It's also a pretty good idea to
make going to Confession a regular part of your spiritual regiment.