It depends on the university you’re planning to apply to. Some universities – the more competitive ones (think Ivy League) – ask students to submit their entire “Score History”, meaning you’d be sending ALL your scores – the good & the bad. Other universities only ask you to send your best scores – meaning you could’ve taken the tests 10 times but you’d only be sending your best 2-3.
With that said, 3 is the norm. More than that can just prolong the process.