Make sure you get the header pins and terminals on the correct side, the one with the outlines of the terminals on it. The most common mistake is soldering on the wrong side of the board.
I like to set the headers on the AVR like this. If you are removing the AVR to program, you aren’t as likely to be bending pins.
Fit the AVR and pins on the board
flip over the board and solder the bottom pins on the PCB first.
Then solder the AVR. Don’t heat the AVR up too much.
remove the AVR.
Slide the terminals together before putting them on the PCB. The blue terminals are a bit harder to slide in. I line them up like this picture then rotate them into place while holding the pins the in holes.