Hello, Sheena! Welcome to WikiTree!
I see you are a Guest Member, so you won't be able to do much yet. However, according to this link ( http://www.wikitree.com/wiki/Member_Types ), you should be able to edit your own profile.
You should see several green-shaded tabs in the middle of your profile, just below your name; one of those tabs says Edit. Click that tab and go down to Last Name at Birth; just after the name you entered (Bradshaw), you should see a green edit link. Click that edit link and follow the instructions to correct your LNAB!
If you still have trouble, let us know here in the forum.