At the wiki page of the stata plugin it is mentioned that it supports different database drivers. Default it chooses a SQLite database. But that one is indeed limited due to technical reasons. So choose one of the others.
See
https://www.dokuwiki.org/plugin:strata#database_drivers
For more info about the 13 columns limit, see this issue report, it is nicely explained by the author:
https://github.com/bwanders/dokuwiki-strata/issues/14