In addition to what John said, make sure you keep the contact info for the PT you shadowed (full name, email and/or phone number). When it's time to apply, you'll most likely need the hours verified by the PT you shadowed, and to do so you still need to be able to contact them. Since you won't be applying for at least 2 more years, make sure you don't lose that info 😛
Also keep yourself updated with the school(s) you're interested in applying to...since it's 2 years away, they could change the number/type of hours required. For example, one of the schools I applied to used to not require verification or a certain number of hours during my senior year of college, and then when I applied that following summer they changed it to 40 hours and verification required. Since you're way ahead of the game too, try to get some other observation experiences in settings you haven't been exposed to yet...it'll strengthen your application and give you a better idea of what else PTs do. Plus, you may decide later you want to apply to other schools, and they might require a certain setting.
Good luck!