I like to play video games. Please tell me if this sentence is correct?
Hello guys,
I like to play video games. Please tell me if this is a correct way to tell a friend: "Good job showing those newbies how to play. Even if you've lost I'm sure you did well."

Question

Answer

Your heading is not correct, because you should not use a question mark at the end of a sentence that is not a question.

You can either say:

"Is this sentence correct?" (DIRECT QUESTION)

or

"Please tell me if this sentence is correct." (IMPERATIVE MOOD)

Answer

"Even though you lost" (in the past) or
"Even if you lost" (in the future)

Otherwise, the sentences are good.  Well done.