Having a mammogram at 34...good or bad idea?

I had my first diagnostic mammogram/ultrasound yesterday, and I'm 34 years old. My Dr. ordered it due to pain I was having on the side of my lft breast and suspicious lump under arm near breast. They took two shots of each breast, then came back and to an extra shot of the lft breast. The radiologist concluded that everything looked normal and the lump was actually just a irritated lymph node. I asked the radiologist about the xray pic' including the extra one on the lft breast and he assured me that they use only a small amount of radiation. I was upset, initially, at my OBGYN who suggested the mammogram (due to my dad's mom dying of breast cancer at age 55) and thought she should have just ordered the ultrasound. I'm not due for my next mammogram till age 40. Even though I now have a good baseline and I now know I have dense breast tissue, I still regret having the mammogram done so early, especially since everything was normal. You hear all these stories about mammograms and radiation. Do you think I am over reacting or should I be concerned?