working 20 days in a row

i told my manager a month ago that i needed to step down from ssv to barista because i was offered a new job with better pay, but that i would still stay at starbucks for ASU. he told me he would give me at least one day out the weekend off so that i wouldn’t have to work 7 days a week, since the new job requires me to work 9-5 monday-friday. my start date for the new job is next week, and he has me scheduled for the next two weekends, meaning that i will be working a minimum of 20 days in a row. he also hasn’t hired a new ssv yet, meaning that every single shift i’m scheduled is a keyholder shift, so that limits my coverage options to about two people.

i’m losing my mind. i don’t know what to do or how i’m even going to be able to work that much consecutively. any advice?