Hi Okrah :) 

Welcome to OpenStreetMap and thank you for wanting to improve Greece :) 

Please note that you have added buildings which have been already mapped some years ago, and an odd way.  For example, see this gas station building and the surrounding area: https://www.openstreetmap.org/#map=19/37.997371/23.696289&layers=D buildings have other buildings on top of them.

Have you downloaded the data of the area in JOSM before starting mapping..? I'm going to revert this changeset and a few more after some days. Maybe you would like to start mapping some of the unmapped villages outside of Athens first..?  We certainly welcome new editors, they are many things to map :) 

If you have questions, feel free to ask either at the forum for Greece  https://community.openstreetmap.org/c/communities/gr/68 or at the Matrix channel https://matrix.to/#/#osm-gr:matrix.org or send me a message.

Welcome again and happy mapping :)