One word for the first time you ever gallop...............saddle, preferably western with a horn to hold on to.
I started riding horses on my own when I was about 4, started bareback when I was about 7 and didn't build enough balance and confidence to try running bareback until I was about 12 or 13. Just take your time and don't force yourself (or let anyone else pressure you) into doing something that scares you. Work your way up to it. Do you maybe have access to a synthetic western saddle that you could take to the beach without much worry about water damage?
Oh, never mind, I don't know how easy western saddles are to come by in Scotland.
My best advice is just to work into it. Start with a canter that you are completely comfortable with then ask for just a bit more speed, then when you are comfortable, ask for a bit more and just keep that going until you are flying.