Would this confession be valid?

If a priest prematurely says the prayer for absolution, is the confession still valid? Is the confession still valid even when the priest is not wearing his normal vestments? Or if I didn't say the prayers the priest asked me to pray until I got home because I couldn't focus during the mass? Is it necessary for a penitent to bring up unconfenssed sins the next time they receive the sacrament of reconciliation?