the crosshair should line up with where the bullet goes, this is most likely just a bug and I'm currently looking into fixing it.
regarding the performance, the game is heavily gpu bound due to all the post processing so I'm planning to add more graphics settings to help alleviate this. I get over 300 fps on a 2070 though, so I'm not sure why it's performing badly on your machine. maybe check that vsync is off?
edit: the aiming bug has been fixed! I've updated the download with the fixed version and also made some performance fixes.