Carl,
We have a completely revised SCLogin module coming in April that's Bootstrap aware and just looks flat out 1000% better than the current module. In the meantime, if you add the following to your template's CSS file, it will set the width to be more appropriate:
#form-login-username input, #form-login-password input {
width: 160px;
}
Hope that helps, but should you need anything else, just let me know.
Thanks,
Alex