The root verb is Bastare.
Bastare wants and indirect object, so it works like MI PIACE, MI MANCA.
MI BASTA X means that X IS ENOUGH TO ME.
so literally MI BASTO means "I am enough to me", and it is a different meaning, not correct in your case.
This sentence: "Do not fear, I am enough"
I would translate it as "NON AVERE PAURA, BASTO IO"
the difference in the meaning is:
IO MI BASTO = I am enough to me (subjective)
IO BASTO / BASTO IO = I am enough (objective)