I’ve seen a lot of comments from colder climate runners that they felt much colder than normal for the temps at Disney and chalked it up to the higher humidity resulting in the temp having more “bite”. Hopefully you’ll be fine, but I’d suggest being prepared just in case.
I tend to be susceptible to cold and start wearing tights, long sleeves and gloves in temps many here consider singlet weather. To help with this, I buy 10-packs of Mylar blankets on Amazon for ~$10. They’re not the warmest, but they get the job done in the corrals and they come in such small, compact packages that they fit easily in a pocket if they’re not needed. Even if you don’t want to hold onto an unused one through the race, you’re only out a dollar if you choose to toss it.