I’m worried I have breast cancer

I F27 have found a lump on my left breast. It feels like a small, round eraser head on a pencil. It is very close to the surface and if I take my fingers I can pinch it and feel all the way round it. It doesn’t move. 

I went to the doctors last week and they weren’t sure what it was, so I have an ultrasound on Friday. This is my first ever health worry and I’m incredibly anxious it’s cancer. It’s just a hard mass, and every page I read online points in the direction of cancer. 

I‘ve had to book the whole day off work on Friday. I’m scared they will tell me I have to have a biopsy and have to wait even longer for the results. 

I really want to start trying for a baby in the next 1.5 years - 2 years and I’m petrified this will postpone it.

Do you have any advice?