In my experience, first time dog owners come in for a lot of criticism. Remember at baby groups, when there were those annoying parents who would ask incredulously "gosh is he not sleeping through yet? Mine is such a good baby. He sleeps 12 hours, plays on his own and is playing mozart on the piano by now". This is a similar situation. Smug dog owners will make comments that unnerve you.
You are learning. You have the self-awareness to ask for help. You have puppy blues. This is all normal.
Dial back your expectations. Treat the puppy like a young toddler. They need regular naps and help to enter new situations (nothing wrong with carrying the puppy, they will feel safer then and the other humans will look less gigantic).
Some dogs are naturally more cautious than others, and with loving support they learn to take things in their stride even if they are never the ones who instigate play with other dogs.
Repeat the exposure to situations with lots of positive reinforcement. Something as simple as holding the puppy in your arms, standing in your open doorway and watching the bin lorry go by, is a good learning experience.
Your 1-1 trainer will help you learn as much as your puppy.
Good luck, and remember: it's your first puppy. Stay aware of your lack of knowledge and ask questions. No-one becomes an experienced dog owner without having a first dog experience.
Essay nearly over. Ask on your local facebook page for recommendations of good dog sitters who offer careful puppy socialisation (not the puppy creche that puts 20 dogs in a barn...). My sitter offers 2 hour sessions of very careful gradual introduction to the adult dogs she cares for who she knows are great with puppies.
Proud dog mum here, my previously very timid dog who would not walk beyond the driveway, took time to socialise but is now an adult, self confident and very caring towards puppies, he teaches them to play and intervenes if he senses another dog is getting too boisterous. These are the dogs you hope to find, to give your pup confidence.
If you are near Cambridgeshire let me kniw, I'll pass my sitter's details to you.