Keep in mind that it is a simple thing but can be held against you and cost you your status, so report to your IPO immediately. Also, not only stems but other majors also can not stay more than 90 days without employment. So it is not true that if you're are a non STEM major then you get to stay 1 year without reporting. you have to report . good thing is they don't keep checking on you if you're working or not, but that does not mean you can get away not reporting your employment. please report asap.