When I load my world its just a void

Me and my friend spent hours building a Minecraft world which we were proud of just to sign in the next day and it’s nothing but a void you can’t even move. We were playing on a Old world and when I made the world infinite it fixed the problem but I don’t want a infinite world.
I want a response on how I can fix this problem immediately as I would like to think I didn’t spend hours for nothing