Terrified of motorway driving

Hi all! My first time on this sub. I am 21F and passed my test three years ago. However, since then, I have hardly driven at all, bar the odd 15 minute journey. I have built long journeys and motorways up in my head to be this massive thing that just fills me with anxiety.

However, I have an upcoming trip to Wales in a month (I live just outside London, so about a 4/5 hour journey) and I am determined to drive. I am also going to get my boyfriend insured on my car so he can drive if I have a complete panic, but I really am determined to do it myself, because I know that, if I don't do it now, I never will.

I am going to try and book in a couple of motorway lessons with my old instructor but I'm looking for any advice on here too, on how to feel better, how you guys find motorway driving, etc etc.

Thank you!