I found out I was pregnant by taking a home test on March 7, 2013. I had intercourse on Jan 28 while I was spotting. I stopped spotting after that day. I have irregular periods every month so I went in for an ultra sound on March 11. They said I was 4w and 2d. Later that week they called back and said it was rare to see an ultrasound that early and for me to come back in. Does that mean I conceived when I had intercourse on the 28th? I know you can ovulate at different times.

If Jan 28th was your only intercourse, then sure, you got pregnant sometime within a day or two (or possibly 3) of then. It sounds like someone wrote down the wrong numbers on your chart or wrote down the wrong guess about age of fetus. Conception date is a guess, and it's based on averages for usual ovulating times after your LMP.
Based on 1/28, you were about 6 weeks pregnant on 3/11.
But it's unclear from the way you write if that was your only intercourse.