汉译英:其实我可以表现得更好的,只是这是我第一次参加,有些紧张。

Actually I could have performed better. It's just that I got nervous as this is the first time for me to participate in such an event.

Actually I could perform better, but I was a little nervous because it's my first time to play/ take part in/ participate.

In fact I could have performed so much better, only that I was a bit nervous because it was my first participation.