Blukkie,

Try increasing width of the form.

Go to admin panel>>appearance>>edit theme>>css.
Add following piece of code:

.ow_superwide {    overflow: hidden;    width: 85%;}

Save changes.
Refresh your join page. Does everything fit now?
If nothing changes go to ow_includes/config.php  file via FTP or control panel and set DEV mode to "true". Save changes. Refresh your join page.

If this helps and everything fits on your join page, check all other pages of your site as well.
Do they look ok?
You need to check all other pages because .ow_superwide  is a site wide class and is used for other pages as well.

Thanks Aliia! 

Works perfect directly after a simpel refresh. :)

Hmm seems I didn't look that good.

On profiles the class gets too big and doesnt fit together with the side bar. So the site is putting it down like here

How is it possible to do the '.ow_superwide {    overflow: hidden;    width: 85%;}'  only for the join page?

Blukkie,

Remove CSS you have added before.

1. Add new class in admin panel>>edit theme>>csss
EX: .ow_superwide_join_page {    overflow: hidden;    width: 85%;}

2. Assign this new class to join page instead of ow_superwide: join_index.html ( ow_system_plugin/base/views/controllers)

WHAT YOU HAVE: {block_decorator name="box" type="empty" addClass="ow_superwide ow_automargin"}

WHAT YOU SHOULD HAVE : {block_decorator name="box" type="empty" addClass="ow_superwide_join_page ow_automargin"}

Do the refreshing and DEV mode if needed to see the changes.
Check your join and profile pages.
Should work for you.