今天我在购物中心买了衣服。

The easiest way to fix this is to add a “了” to turn this sentence into past tense

买我买了二种袜子和一条裤子。

Don't forget to add yourself (我) as the subject of the sentence!

我想买一件棉外套而但是那件太贵了。

我今天我在去了购物中心买衣服。

买二我买了两种袜子和一条裤子。

When using measure words, you use 两 instead of 二 to say two of something (for example 两个小时 instead of 二个小时 - two hours).

Another measure you could use for socks is 双, meaning "pair." To be honest, 两种袜子 sounds a bit strange but it's also technically correct. However, I'm not a native speaker, so I might be wrong.

想我想了买一件棉外套而可是那件太贵了。

今天我在去购物中心买衣服了。

买二我买了两种袜子和一条裤子。

我想买一件棉外套而那件的，但是太贵了。