Their first season in this competition is more about gaining experience and understanding the intensity of competition that takes place in the UCL with against big teams, so indeed they can't do too much in the UCL when facing strong teams, like as Feyenoord, PSG and eindhoven who have experience and better performance in the UCL, however, like your said, the experience Girona have gained from UCL games this season will be invaluable for their future development, although there is no guarantee that they will be able to qualify for the UCL again if remember their inconsistent form in La Liga so far.
I feel that Girona did not do so well in the UCL this season of we look at how strong they were in the La Liga last season. I had expected them to be at the same level as Aston Villa who have been doing very well bith in the Champions league and the league as well but Girona is neither doing well in the champions league nor the La Liga. Assuming they were able to qualify for next round, they would have raised more funds to bring in some new faces to the club next season.
As @Palakka said, it doesn't matter if Girona has a bad performance this season because this is the first time Girona has competed in the UCL. Certainly Girona does not have the experience to manage the team as well as possible to perform consistently in several competitions.
And previously I also said last season that Girona good performance last season was just luck when the top teams were busy competing in more prestigious competitions and Girona was able to take advantage of the opportunity well. I also said that this season Girona will definitely have difficulties because the top teams are trying to improve their performance and Girona will not be able to compete like last season.
So there is no need to expect more from Girona to have the same level as Aston Villa.