Should I chapter or just accept a new mos I don't want after failing Army AIT? How do I have to stay out 6 months if I chapter out?

It could certainly be longer than six months out. Prior service serves at the needs of the Army. The Army is a career, and you don't always get the entry level job you want, but you almost always retire somewhere you never imagined.

So, if you want this to be a career, then stick with it. Otherwise, find a career that will give you an annuity at 40%+ of your base pay for the rest of your life after the first 20 years, plus matching 401k, cheap Healthcare for life and 30 days of paid vacation every year and a housing allowance based on your location while you're working.

But hey, if you want to work at Safeway or spend 30 years paying off student loan debt because learning about how organophosphate poisoning overstimulates the parasympathetic nervous system and how acetylcholinesterase counteracts that - I understand. Who really likes applicable science anyway when you have a promising career doing.... That thing you were doing before the Army.

It's a job and a career. You do it because it feeds and takes care of your family. There are plenty of routes for progession and advancement.

Look Corey, it doesn't matter how hard the course is, other folks passed it, you didn't. Regulations state that any AIT failures will be sent to a new MOS for the "good of the service" not what you want, but what is needed. If you decide to forgo the Army's choice, then they can chapter you out as a failure to train. That means to TRY to re-enter any service you will have to ask for/get a wavier- that takes time and is NOT guaranteed to happen.

You will not be guaranteed to be able to get any waiver necessary to reenter the Army in 6 months. All you have to do is use the search function and see how well it didn't work out for others who believed all they had to so was take the chapter and they would be given a waiver in 6 months.
Stay in; become a Chem Dawg (74D), try to get additional training while at Leonard Wood (Recon, etc).
You may be able to reclass upon reenlistment, not within a year.