Should I lie to my friends about my fortnite wins?
That seems pointless. Why would you lie to your friends about your Fortnite wins?
I want to sound more accomplished
You need to be more honest when it comes to your friends. You are being selfish and trying to make yourself sound better than you actually are.
Maybe but come on, they  might think I am cool.
They will until they play with you and realize the truth. Then they will feel hurt that their friend lied to them. So just be honest or learn to play really well so it won't be a lie.