Well, it definitely doesn't sound to me like you're over-reacting. I think that once you've apologized for a minor slight, it can be put to rest. That being said, your feelings are still valid even if you were to be over-reacting...and when you feel awful, it's difficult whether you've reacted appropriately or not.

You may not be able to change how your mother feels, but you can try to adjust how you let this impact you. You are NOT worthless and you deserve all the care and consideration in the world. If she makes you feel worthless and you hate talking to her, are you thinking about changing the situation at all?