My opinion, don't do the 13/14 mile run this weekend. We're too close to race day at this point. It takes 7-10 days to fully realize the benefits of a single training run, and about 4-6 weeks to fully realize the gains of training week. The 13/14 mile run you would do this weekend will cause more physical harm than it will physical benefits. Assuredly there could be some mental gains from it, but my opinion is those mental gains would be outweighed by the recovery necessary from it. You may still be feeling some aftereffects from the 13-14 mile run physiologically by the time race day comes up. If you've been doing your training runs around a 15 min/mile, then the 8 mile run has taken you about 2 hours. That's a sufficient endurance run to prepare the body aerobically for completing a HM.
Presumably the 15 min/mile pace is not all out effort either if the Garmin has been suggesting an appropriate training pace for long runs. So if you attempt to run at a 15 min/mile pace on race day, then you should be more than fine to cover the 13 miles. This assumes that the 15 min/mile long run pace is appropriate. Have you done any other races recently that would be a good judge of current fitness?
This is the most recent POT and estimate corral assignment educated guess.
Your corral assignment depends on what you put for the estimated finish at registration. If you put 2:15-2:30, then you'll be in Corral C. If you put 3:00-3:15, then you'll likely be in Corral F. I just went into my race registration for Princess 2023 and can see what I put. So you should be able to log in to your runDisney account and see what you put for your estimated finish. Then use the chart above to get a pretty good idea where you'll be slotted.