pirated game leading to problem

hey so i have a macbook neo bought it like 2 weeks ago

the problem is i downloaded a game from a priacy site wont name it but it starts with a "n"

opoened the game it ran good but the problem is now the audio is worse on youtube and even while opening new tabs it lags a little
opening apps also lags a little bit

i deleted the game but i wanna make sure i did the right thing can anyone tell me how to completetly make my mac normal again and make sure the app is deleted for sure