My unpredictable work schedule makes making plans with friends hard

For context, I typically work 4 or 5 days a week in the afternoon, and in the morning I’m at school. I am on a list where I am at the very top of a call list to cover shifts. My mom asked to put me there as my family is financially struggling. I really want to spend time with my friends and make plans with them on days where I think I am not working, but then I often have to cancel last minute because they ask me to work on a day when I’m not scheduled. My friend is often disappointed in me when I cancel plans last-minute, and I try to comfort them but often times there’s not much I can do about it but negotiate for another time we could do the same, once again with the unpredictable risk that I could be working that day. Their disappointment then turns into perceiving me differently and usually viewing me as less of a friend or they lose their interest in doing things together with me whenever I am free. What should I do so that I can make plans with friends without this aspect of uncertainty?