What will be my best option to have legal child custody of my child?

You should consult with your own attorney so that no missteps are taken. They are not looking out for your interest.

To answer your questions: I have a child with my ex; currently we are still both living with his parents. We went to a bank notary and gave his parents temporary custody of our daughter. First, is that even legally binding or legal? It's legal, meaning there's nothing illegal about it, but it's not necessarily legally binding. Secondly, if I move out without my daughter until I get stable, can they call that abandonment? Yes, even if they lie when they claim you abandoned her. Courts find it easy to believe you abandoned the child, as opposed to left her with your parents temporarily while you get your life in order. Frankly, the situation you set up is a common and typical way that grandparents try to take custody away from the parents, i.e., by claiming "our worthless daughter dumped her kid with us, and we selflessly sacrificed to care for the poor waif, with whom we've formed a loving bond. So now we wish to adopt the child and terminate the mother's parental rights." The "custody" agreement is only for a year, but I'm trying to get on my feet and don't want to be blindsided if they decide to try to keep her from me. I trusted them, they said everything was legal but the way they've been treating me lately, I'm having major doubts. You're wise to have doubts, for the reasons I've covered above.

It is legal, but it is only as good as long as you consent. When you give them written notice that you are revoking the power of attorney, then they will probably file for guardianship. Prepare for it, but get yourself straight first, then find an attorney that will fight for you to get your child back.