我的包是Mary的3倍大，我的包比Mary的大2倍。（翻成英文）

比较的有三种句型。
1.倍数 time(s) the size of
2.more than 倍数time(s)一个形容词比较级
3.倍数 time(s) as 形容词 as
所以，你就可以任选其中一个…
如：My bag is three times as big as mary's.

my bag is three times as big as mary's.
my bag is two times bigger than mary's.

My bag is twice as big as Mary’s。