Found a hard lump in breast

My husband discovered a lump in my breast a few days ago, and I had no idea it was there! The last time I checked myself was about 2-3 months ago. The lump is quite large and hard, and I don't think it is movable. I'm 45 years old, and I'm feeling scared. I have a mammogram scheduled for next week.

From what I've researched so far & the look and feel of it, Im thinking it is cancer. So worried!