Brighten Portion of Image?

[tspence]

Can't figure out what I'm doing wrong.  Trying to lighten the face of the girl in the attached.  Steps I took:
Duplicate layer.
Use ellipse tool to select face.
Adjust selection as needed (see attached - overbrightened for emphasis).
Use eraser tool - fuzzy brush at 30% or so opacity - to get rid of line between adjusted and non-adjusted part.  Here is where I get unintended results.  Why is the eraser making a white path?  Shouldn't it fill the erased part with the full image underneath?

What am I going wrong?

Thanks!