This is certainly a valid confession, as it was sincere at the time.
So long as the penitent is sincere then it is the responsibility of the confessor to ensure that the confession is valid. See my question in this forum:
Is it the confessor’s (priest’s) responsibility to ensure that a confession is valid? and also Fr Serpa’s response to
Was my Confession valid?
The only caveat would be that, if the gestures were grave matter (ie. mortal sins), then you should have mentioned the gravity of the sin and the number of times that you made these gestures. Your confession as described gives the impression that they were not grave matter and the confessor would have accepted the confession as such. Therefore, if they were grave matter, then your confession is valid, because it was sincere, but you should mention the sins again, and the number of times, in your next confession, just saying “I innocently forgot to mention the gravity of these sins in my last confession”.
However, if they were not grave matter, then there is no need to have any second thoughts about this confession. In confession we often describe a venial sin which we are conscious of in general terms (eg… “I have had proud thoughts”) without thinking of specific instances.
I would recommend that during preparation for confession that one think about specific instances of the venial sin, but failure to do so would not invalidate the confession.
