You end up in Positano, so yes, you can walk back, catch a bus to Agerola or, like I did, hitchhike your way up.

Hitch-hiking is perfectly safe in Amalfi coast and quite easy to get a lift.

Typically at the tiny bus stop just outside Positano on the main road, cars slow down significantly as there's a bend and you can try your luck there.
Or ask for the local bus.