Size of the calender

Hello.
You can change the size of calendar in the Booking Calendar shortcode in the option parameter. For example:
[booking type=1 nummonths=2 options='{calendar months_num_in_row=2 width=568px cell_height=30px}']
Please check more here https://wpbookingcalendar.com/faq/shortcode-booking-form/
Kind Regards.

Thanks! And how can I change the “send” text button to something else

Currently it’s possible in the paid versions of Booking Calendar.
You can test it here https://personal.wpbookingcalendar.com/
Kind Regards.

Yes I have the paid version. But how and where can I change the text of the Send text button?

You can configure it at the Booking > Settings > Form page in A way like this
[submit class:btn "Submit"]

Please use shortcode generator at the right side of the Booking > Settings > Form page for the fast and correct creation of booking form fields.
Watch it in this video guide https://wpbookingcalendar.com/help/booking-form-fields-settings-video-tutorial/

Just be sure that you was not activated using “Simple booking form” configuration at the toolbar at Booking > Settings > Form page.

PS Please note, this forum is only about support Booking Calendar Free version. Relative paid versions, please contact here https://wpbookingcalendar.com/contact/
Kind Regards.