Should I ask for a biopsy anyway?

this weekend I found a hard lump in my left breast and went to see my doctor today. He wants me to go in and have an ultrasound done because of my age a mammogram was not recommended. He said depending on what they see that he might want to take a biopsy. I I just know myself well enough that if I don’t have a definite answer as to what this is or what it could be that I am going to drive myself insane. Should I ask to have a biopsy done anyway because I don’t think I would be able to be at ease without knowing 100%?

Background: I I am 20 years old, and have a history of breast cancer on my mom’s side in my extended family.