why do i feel so guilty?

so, when i quit my job in july so that i could be the mother that brooklin deserves, my employer asked if i wouldn't mind filling in a day here or there if they needed me, just until october when they would get the okay to hire someone to fill my position. i agreed, thinking that it would be no big deal, and it would be nice to have a little play money every once in a while. well here it is october heading into november and they asked if i'd work for a week next month. a whole week, not just a day or two. i was already beginning to dread the single days, but now they wanted a week, and in november, which i might remind you comes after october. i really didn't want to and i had a hard time saying no, so i came up with a lame excuse/white-lie so that i didn't have to tell them that i just really didn't want to. i feel really bad, not so much about the partial dishonesty, but about the fact that i'm not wanting to help them out. i know that if i did go in to work i would be absolutely miserable and i'd be complaining the whole week and probably the whole week prior. why do i feel so bad? i quit. and i did them a favor by filling in a few days this summer through the month of october, like i said i would. so why can't i tell them i just want to be done? i have another, more important job, and i don't do too well when i've got too many things on my plate, just ask my husband. i know i shouldn't feel bad, because i could have said no to working at all after i quit, and i was doing them a favor. but i still do.