Hoy hice mi examen de la música.

Creo que me fue bien, pero en la primera y la segunda obras hice lo/cometí el máximo errores.

"Cometí" is supposed to be the right thing to say here, but you can also hear "hice" in the street or when you talk to your friends. I think your sentence is probably the only situation where I'd use "cometer." Most of the time I'd use "equivocar." For example, instead of saying "cometí un error," I'd say, "me equivoqué." If for whatever reason I need to ask who made a mistake, I'd say, "Quién se equivocó?" or "quién fue?" (if the people I'm talking to know what I'm talking about.) I wouldn't say, "quién cometió el error?" It sounds too formal to me. People in the street might also say, "quién hizo el error?" or "quién lo hizo?" (I'm including this just because it seems like you're aiming at the real language.)

Al fineal del día, estoy orgullosa de mií.