Problem with size of Description field in Web Forms

Problem with size of Description field in Web Forms

I have successfully created a web form under "Cases" to submit a problem on my web site. The problem is the "Description" filed seems to only be abut 100 x 50 pixels and I don't see any way to change the size of the entry field. There is a "///" in the bottom corner but it can not be accessed in the design form (see attached), and it does not exist in the final form. I would like to make this entry field something like 300 x 200 pixels or larger. Any help would be great - thanks.