How can I adjust the width of the calendar widget on the side bar?

Hello,

This is Stephane from Paris, France.

I just bought Appointments + and installed it to test it on :
http://www.coquettissime.fr/bp-maquillage/

I put the calendar as a widget on the side bar but it is too narrow. As you can see, the calendar only takes half of the width of my sidebar.

How can I increase the width of the calendar so that it takes the full width of my side bar?

Thank you in adavnce for your help,

Stephane