9month old retriever being dominant

I live in UK and have a 9 month old golden retriever male. He has “warned 2 people in the last 2 weeks in a coffee shop I go to every day with him. They bent down to stroke him and he snapped (no contact). I never told him off and removed him (apologised of course). He also has growled at my husband when he went to clip his lead on. He’s a really big boy and I find him intimidating if I’m honest. I took him to the vets to get his anal glands checked today and he went for the vet (I totally get it’s a horrible thing to get done). My daughter lives abroad and will be coming home for Xmas and I am worried he will be funny with her - I am trying to get a trainer and I’m under no illusions I know I probably give off stress vibes. I am feeling quite stressed anyway due to my lovely mum passing away but that’s another story and I feel out of my depth with him. We love him dearly and he’s quite spoilt - I admit that. Any advice please