Hello.
1.You have already asked about the centering of the calendar and we have replied to this issue here https://wpbookingcalendar.com/support/comment-page-92/#comment-27732
Please follow that instruction about how to make it centered.
2. Also, you need to remove this code, that you was added early:
.booking_form .booking_form_div {
text-align: center !important;
}
3. Relative customization of the booking form, check more here: https://wpbookingcalendar.com/faq/change-labels-colors-in-booking-form/
4. 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/
Kind Regards.