Due date question (probably really stupid)

Hey all! So just took three tests this week and they all said the same thing. I'm pregnant.

I'm nervous and excited and a little bit freaking out inside haha. So my question is probably really dumb but this is all new to me.... I am 95% sure of when we conceived since we've been only having sex on the green days in the glow app 😊 so I am pretty certain it was between July 3-7 since we had sex every day and we literally did not have any sex between my last period and then. SO... The app says I'm 4 weeks pregnant but that the fetus is only 2 weeks.... But wouldn't I only be 2 weeks pregnant? Why is there a difference in "how pregnant" you are vs the age of the fetus? I feel like I'm missing something obvious and am feeling really dumb but if we conceived around 4th of July, how could I be 4 weeks pregnant?