‍▲你的句子其实没有错。查了一下2010年高考英语的扫描版，原句为：

It was a chance of a lifetime to win the first…

答案是将 chance 前的 a 改为 the。the chance of a lifetime 是英语中的惯用表达，意思是“终生难遇的机会；千载难逢的机会；一生中难得再遇到的机会”。如：

It's the chance of a lifetime. You shouldn't miss it. 这是一生中难得的机会，你不应错过。

It would be foolish to let such an opportunity slip; it's a chance of a lifetime.  坐失这个良机，那是太傻了，这是一生中难得的机会。

Then came an invitation to Martinique , an island in the French Caribbean. It was chance of a lifetime.  然后被邀请到法属加勒比海的马提尼克岛，这真是千载难逢的机会。

▲类似的表达有 the experience of a lifetime 是英语中的惯用表达，其意思是“终生难遇的经历；千载难逢的体验”。如：

This could be not just the trip of a lifetime but the experience of a lifetime. 这可能不仅是一趟终生难遇的旅行，也将是一次终生难遇的体验。‍