First name field for newsletter widget in sidebar is too small

Hi! My site is not live yet, but I\\\’m using the Hello Boho theme. I\\\’m using the Genesis News extended widget in Primary Sidebar like was in the demo, but I don\\\’t want the last name field, only first name. When I select only first name, there is this weird empty space where the last name used to be. Is their a way to make the first name field stretch across? I tried to attach a photo that was first PNG and then JPG and it said “upload file type not allowed.”