Am I overreacting?

Hi all, 

three weeks go I found out that I had breast cancer, I had an ultrasound done after the dr felt a lump in my right breast.. Turns out I had two lesions and the original one I could feel was benign and the smaller one that was only picked up on ultrasound and they assured me didn't have any characteristics of cancer was malignant..as you can imagine it was a massive shock esp as I am only 32 years old..

a week later I had surgery to remove the affected area and my lymph nodes were checked.. Great news is it hasn't spread, it was a grade 2, hormone positive her-2 negative. I see the oncologists next week. 

I am so scared that a cancer cell is still lingering in me and that maybe another lesion that they missed is starting to form..to the point where I really want chemo even though I probably won't need it just to be 100% sure it's been blasted.. 

Are these feelings normal or am I over reacting?