So understand the low points. I have had them for every single Halfy and the full marathon I did last year. The full marathon was the worst! I was running for the the BabyLossNZ charity when we suffered our second miscarriage, just 4 weeks prior to the race! I was doing tertiary education which had to be requested for aegrotat and still grieving our first baby loss. Was bloody awful and a full blown meltdown.
Reach out to those closest to you and talk about it is my biggest advice. The anxiety is there because you care, always remember that and take some energy from being a good person. I agree, you'll get there mate, and aiming to finish is absolutely fine. Remember what you're doing this for too. It's not really about the running at all, that's just a vessel. The charity awareness and support goes further than you know and is what fills the vessel, and you should be proud of what you're doing and effectively 'paying it forward'. All the best mate.