Hello Beth and welcome to the Wix Code community.
Wix Code does not allow modification to an element’s size and/or placement.
Therefore in order to achieve this you will probably have to use a non-wix code solution.
For example you can use a full-width gallery with the shape as an image.
Another option is to set the shape as the background image for your page.
For further assistance regarding this please contact Wix support directly at support@wix.com