Puppy has become shy and subdued around people, help?

Hi all,

We picked up our 11 week old collie x golden retriever puppy 5 days ago. She is so sweet and well behaved and very much locked onto my partner and I bonding-wise. The breeders kept her and the siblings in the kitchen, and in the house there were both dog parents, three adults and a 5 year old child that frequently got into the pen with the pups – as such she has been exposed to a LOT of noise and stimulus, which meant she has been a confident and social puppy from the start (came right up to anyone who came into the pen, desperate to play etc). She has been a very confident puppy at home (haven't seen tail between her legs once, loves investigating new areas and she sleeps soundly through the night). She has also been confident with the people we introduced her to at the start. To work on her socialisation we took her to the garage yesterday and asked the blokes to offer her a treat (she was in a sling), which she took but seemed quite subdued. Later on she met my partners dad who is a big bloke and she didn't want to go near him and refused to take a treat. We weren't sure at the time, but we are worried these interactions caused a 'negative experience'.

Today we took her into the village in her sling where she seemed very subdued and a bit overwhelmed from the noises and talking to a shop owner. Later on she refused to take any treats from someone who stopped to talk to us. There were no forced interactions (always let her refuse the treat). When we got home our neighbour (who she met early in the week and seemed fine) was there and the puppy was pulling away from her too, also refusing to take any treats.

This shy/subdued behaviour seems to be a change compared to how she was when we picked her up. Have we caused a problem here, and can it be fixed? We have been trying to make sure we get her socialised, which we didn't think would be a problem given her original temprement, but feels like we may have set her back? We are really hoping this is normal for a puppy at this age (the fear period) and that we just need to keep working on the socialisation (perhaps more carefully/slower now). We are taking her to puppy classes starting Monday, so want to make sure we know where we are at going into those and get it right!

Any help, advice or reassurance is really appreciated.

Thanks, Two first time puppy parents.