This is a "bug" within cPanel; cPanel is detecting that PostgreSQL is installed, and since it's set to allow two databases of each available type, it's thinking you would have access to two MySQL databases and two PostgreSQL databases. At this time however, PostgreSQL is only installed as some of the backend systems require it to be there; we don't have it enabled for free hosting. With the code that does this being a part of cPanel as well, we're not able to edit it to indicate that there's only the MySQL databases available to free users.
The error itself is correct in this case though; you have hit the maximum of 2 MySQL databases, so it won't let you make more that use MySQL. You should be able to install multiple scripts into the same database as long as you are using software that supports "Table Prefixes," however we don't currently have a way to get more MySQL databases available per user on free.