No, it is your choice to serve or decline to serve. If you choose to serve as personal representative you can later resign, although you may have to provide an “accounting” for the period you served. If you decline to serve, or resign after serving, the alternate executor named in the will typically is then appointed by the probate court.
If no alternate is named in the Will, or the named alternates die or are unwilling to serve, or a person dies without a will, the probate court will appoint someone to serve.