Hello.
Here is possible 2 solutions.
1) Please insert the booking form (booking shortcode), at the page inside of the DIV element, like this:
<div class="widget_wpdev_booking" >
... booking shortcode here ....
</div>
Its will make the calendar smaller.
2) Or you can make some fixes in the CSS skin of calendar. You will be need to change the width of the specific cells inside of the selected calendar skin (which you are set at the General Booking Settings page). You can find skins at the ../booking/css/skins/ YOUR SELECTED SKIN .css or ../booking/inc/skins/ YOUR SELECTED SKIN .css
Then you will need to find something similar to this and make your modifications of the width.
/* S I Z E */
.datepick-inline table.datepick td{
width:40px;
height:40px;
padding:0px;
border:0px;
/* font-size:38px;/**/
}
.datepick-inline table.datepick td a{
line-height:38px;
height:40px;
}