Hi SK
My first 10K was a very similar time, also a local race on a course with a few little hills!
I've not done the BUPA 10,000 but it should be pretty flat? Do you have a coloured number that ensures you go into the right pen? I wouldn't worry too much about the start, most of the bigger 10Ks I've done have a sub-40 pen, 40-45mins, then 45-55 mins. So you'd be in the right pen regardless of 50 or 55 minutes. The best races I've done pace-wise are the ones where I've set off slightly slower than my planned pace as it means you spend the later stages of the race feeling good and overtaking others who've gone off too fast!
It took me a few attempts to get under 50 minutes, I think my first 10K I was so scared of coming last that I ran as hard as I could for the whole race! My training then was also three times a week but unlike you, I would just run everywhere at the same pace and wonder why I wasn't getting any faster! I was also clueless about pacing, I would just run without working out what pace per mile or km I should be going at.
Your training sounds much more structured. It's only 2 weeks away but if you have a garmin or similar you could maybe try doing one of your speed sessions before the race with maybe 3 or 4 x 1000m @ 7:55 pace (goal 10K pace) and see how it feels?
Good luck with it, it's brilliant when you do crack that 50 minute barrier 