picking rates

i started my first full day yesterday and i’m kinda nervous because i see a lot of stuff about picking rates. i was told 300+ is considered average, but i was at 225 and felt like i was constantly moving as fast as possible. i also don’t understand how missing items works. i was told if i report 3 things missing in a week ill get written up, and i had more than 3 things missing during my one shift….they literally weren’t there even after scanning literally every item in the pod. what should my pick rate be? and what’s the policy for missing items, do they actually investigate the items or am i just going to get yelled at for something i have no control of?