blow one's lines：忘记台词；念错台词

e.g. There I was in my first major role, and I blew my lines!

那是我第一次演主角，竟然忘记了台词！

e.g. If you blow your lines, just try to cover it up.

如果你讲错台词，应尽量不露声色，继续往下演。