it's fine , ur endgame play wasn't bad , u developped the king and activate the rook , if u just took on f4 when he pushed his pawn , it's winning because after you played king b4 instead of taking on f4 , he was able to create a passer .
but it's fine , we live and learn 
https://www.chess.com/analysis/game/live/81378620580?tab=analysis
I promise im a better endgames player, i just felt like i was in a time scramble