最开始我是知道我的答案的，但是后来我变得迷茫了，不确定我到底是不是正确的。用英文怎么说？

这种情况可以用英文表达“I started out confident in my answer, but then I became confused and uncertain if I was actually right.”

详细解释如下:

I started out confident in my answer:最开始我对我的答案很有信心。I was sure my answer was correct. 我确信我的答案是正确的。

but then: 但是后来

I became confused: 我变得迷茫起来,我变得困惑。I was no longer certain about things. 我不再确定事情的真实情况。

and uncertain: 和不确定的

if I was actually right: 如果我实际上是正确的

所以整个表达意思是:最初,我对我的答案很有信心,我确信我是正确的。但是,随后情况变得混乱和不确定,我开始迷茫,不再确信我的答案实际上是否正确。

类似的表达还可以是:

I started out with conviction in my view but later doubts crept in.

一开始我十分相信自己的观点,但是后来怀疑悄悄产生。

I began confidently but ended up confused.

我开始时很自信,但最终感到困惑。

I thought I knew the answer but then felt lost. 

我原以为我知道答案,但后来感到迷茫。

等等。总之,最关键的就是表达最初的自信,然后产生的迷茫和不确定。这种从确信到怀疑的心理转变,在英语中可以用上述不同的表达方式来 convey。