In Divshot, you can change the size of the input in the 'inspector' section. This lets you select the Bootstrap defined inputs.. input-large, input-xlarge, etc..
You could also define a custom CSS class and use it to specify the width
of your input. Then assign the custom
(you can name it anything) class to your input..
<input class="input-large custom" type="text">
Here's an example on Bootply