I was declared an unfit mother, because I did not show up to a guardianship case, which I assented to. Do I have any chance of regaining my rights?

What was your reason/excuse for not showing up? Regaining your fitness is going to be tough.

Yes, if you were not in the hospital or in a wreck or some reason for not showing up.

If you merely just did not show up, the court will view this as not really even caring enough to show up.

At this point, you may have to do parenting classes, have months of home studies and more, and that is even if the judge will consider allowing it.

You will need an attorney and it will be a hard fight

Without knowing the whole story we can't even begin to know your chances. But it would problably be best to hire an attorney to advise you.