why don't I feel that this is serious?

thanks to you all for your reassuring responses...

I've met today with the oncologist and begin chemo in a fortnight - been told that I have her2+ so having Herceptin for 12 months as well as 6 x 3 wkly cycles of chemo.  Now I'm starting to feel less sure about my future.  Although I was told that this makes it a more agressive form of cancer I didn't think to ask what that does to my chances of full recovery having previously been told that I had about 90%...  the partial mastectomy biopsy showed a clear margin and no lymph nodes involved - who do I ask (now) or do I have to wait until going back in a week's time (when I have a "port" implanted)?  I know that I might sound ungrateful but am beginning to feel really scared!!!