I’m worried they missed the cancer

I Went to the breast clinic a few days ago regarding a hard, small breast lump. The doctor did a physical exam and he said he thought the lump was benign, but he wanted to do an ultrasound to make sure. He drew a circle in the direction of where the lump was and they did an ultrasound. They said it was just normal tissue and nothing to be worried about. He also said that I need to looking to getting a wireless bra because some wired bras can cause issues. During the time of the hospital appointment, I wasn’t actually wearing a bra So I guess he was right? (My bras are too small).

When I went home, I noticed the circle where he drew was not on the actual lump, and he drew it an inch below where the lump was. I do remember the ultrasound went around the whole area (I think?). I’m now panicking thinking he missed the lump? 

What do you think? He said he will write me a letter afterwards too, which I hope will have more info and put my mind at rest.