I highly recommend Oulton Park, i did my first ever track day there last year and like yourself had my worries before hand but it was a great day out...

I did it in an Escort GTi, so not a fast car and i was worried about holding people up etc but it wasn't a problem and i rarely had to move over for stuff tbh, just keep an eye on your mirrors and move over when you can see a quicker car coming through. I did a Novice day but most of the people there where clearly not novices haha but i felt it was going to put me a bit more at ease booking that day being my first time on track....

As the others have said just enjoy yourself, i was taking it steady at first and as the day went on i could clearly see i was getting quicker. I always thought was it worth doing a track day in what isnt a quick car but it really was worth it and i was keeping up with things far quicker, not that i was that interested in that, it's just nice to drive your car fast in safe environment.

I say book it and just go and drive your car to your limits and Oulton is a fantastic circuit....