I want to skateboard and i can ollie fine on rug but when i try it on cement the board moves and stuff?

i can ollie on a rug ok but then on the cement my board moves and the back wheels dont get up i know i am doing the ollie right but when i try it on the cement the board moves and the back wheels dont go up i really need help because most of my friends skate and they are really good and i would like to start skating but i dont know if i am good please give me some tips about ollieing on the cement thanks!