Create a database and make it "current"
In 'psql', you can change the database you are connected to by using the \c metacommand.  So it would look like this:

CREATE DATABASE my_database;
\c my_database
CREATE TABLE my_table (
  id UUID primary key,
  data json
);


This works from '\i' included files.  When the \i file is done, you will be left in the new database unless you do something to change back to the old one.