Is the questioner sinful for not paying the registration fees after leaving her job, knowing that what she paid for her daughter within two months exceeds her salary?

You must pay the registration fees agreed upon with the kindergarten, along with the tuition for the period your daughter attended, to clear your liability; due to the Almighty's saying: "O you who have believed, fulfill [all] contracts," and the Prophet's (peace be upon him) saying: "Muslims are bound by their stipulations," and "Whoever has wronged his brother concerning his honor or anything else, let him seek his forgiveness today before there will be no dinar or dirham."