I'd say stop worrying. There's a long time to go and a lot of training to be done before Paris 2016. Part of training for these things is getting used to running the distance both mentally and physically. It's perfectly normal to doubt yourself at times when training. We all have good days, bad days and days where we wonder why the hell we entered a marathon in the first place!
You'll do it. You've picked a great event to do as your first.
Actually when it comes to me running a PB I'm the least strategically approached person you'll meet.
This year I've ran 5km (twice), 10 mile and half PB's and at no point in any of those races did I look at my watch to see what my time was or pace was until I'd crossed the finish line (this also stands for my 10km PB last year). I also ran my marathon PB this year and I only checked my watch about five times in the entirety of that race. I seem to run better off instinct and judging how I'm feeling than clock/pace watching.
In Paris this year I glanced at my watch at 5km and decided I was running too fast, so slowed down. I glanced again at 10km and decided I was too slow, so speed up! I looked at the watch again at the halfway point and saw I was bang on pace with my 2012 PB time and just told myself 2012 was getting its ass handed to it! I then glanced again at 25km and was feeling great at this point and could see my time was good still. Last look before the finish was at 35km. I knew at that point as long as I was running that I'd PB.
I'm pretty sure every single thing you'll read about running will tell you what I did was wrong, but it worked for me. Also when I ran my 5km PB at the weekend I thought I was going much slower and did stop to give someone a hug mid run! I'm also sure that's not in any of the running literature.
I like the idea of not having to get up early for the marathon in Stockholm, but have some concerns about starting at a time that would see you running through the hottest part of the day. Thankfully it's looking like a coolish day for Saturday.
I don't have a time goal for Stockholm. I just plan to go out and run the best I can and see where I end up. I've been running well, but did spend all Sunday ill and didn't manage to eat a thing all day. I made up for that yesterday right enough!
I'll do a watch check at the halfway point on Saturday. I know what time I need to be through the halfway point if I'm going to have a bash at a good time.