No, you're fine to continue with the method you're using. Be sure to save a Contact (name, title, email or phone #; can be the doc or an office staffer or program coordinator), specialty, and date range, besides hourly totals.
You're fine to do that if you want but just to clarify you won't need a signature for AMCAS only an email or phone number. It's much more relaxed on AMCAS you'll just input your hours, speciality shadowed, doctor, email and maybe a word or two about clinical or surgical days shadowed into one text box for which there are templates on SDN if you just search for them. Space is limited if you have extensive shadowing experience
It's always a good idea to keep your own records, but for volunteering, it's more desirable to have independent records of the hours you commit, through a volunteer coordinator/office, etc. And to keep the Contact information in your records.
