Time to decide if you want to stick it out while trying to find work and explaining the short job, getting fired (might be eligible for unemployment), or quit.

Some startups are run by cowboys/cowgirls. They don't care about anything other than features until everything falls apart or they rebuild in a nightmare sprint.

I've been at one of these. You will fail to change them even if you stay for 3 years. You risk getting fired if the CEO realizes the mess and hires in someone to fix it. Your manager is already thinking about firing you.