several million people这个,对吗?

没错
数百万的人

several millions of people

hundreds of million of people is the better i think

当million,billion等之前出现了数字时，可以不用加s——7million people
但hundred/million/billion后面加了of表示成千上万，成百上千等意思时，就要变成millions of/billions of

这里还应该加上of，连接people