Hello, I am a 17 years old and work at a local grocery store and they want me to work on sundays, I told them it was impossible for me to work till after 1(because of the divine liturgy of-course) and I was planning on making Sundays completely unavailable or trade in the shifts for that day, well since I just got hired i was told I would start on the 14th but after I came home from divine liturgy(All the Ukrainian catholic bishops were in the church, thousands of people, very nice place to be

) I got a call saying I had a shift today and I was late…(I didn’t think i would be scheduled for a shift till the 14th of-course) so in fear of being fired I went and worked for the next 4 hours.
I have 3 questions now, Is what I did working on the sabbath sinful even if I made the time to fulfill the Holy obligation?
Also, If your job requires you to work on sundays is it sinful?
would any of these situations lead to mortal sin?
Thanks, and God Bless.