有两个地方需要改正:
1.ago 改为before,因为ago一般起点为现在.
2.the players had played quite well 之前要加一个that,因为在间接引语中,第一个宾语从句的that可以省略,但是第二个一定不能省略.
综上,修改后的句子为:
Mary told me (that) she had watched that football match two days before and that the players had played quite well.
其中,第二个括号中的that可以省略.