"7. d5 Trying to remove my doubled pawn." You're relying on your opponent to help you out.
"11. Rd1" The only way to polish off your pawn winning combo is to play 11. Bxb8 Raxb8 12. e3 protecting your c4 pawn. Of course with your doubled pawns on the c-file, you don't really have a full pawn here.
At move 19, Kd2 was probably better.
At move 21 you can play Kd2 and you are only down a pawn. It seems like you could fight on in that position rather than resigning.
"12. ... Rxc4 (e3 would have been adequate with the 'discovered' defence of the pawn)" If you had played 12. e3 you would have lost your bishop on c7.
"14. Rc1" There is very little point in defending this pawn since it can just be attacked again a second time. You were probably better off playing 14. e3 Rxc3 15. Be2 and you are ready to castle.
Here is a recent (and surprisingly short) game of mine against a much higher rated opponent. Although I started strongly, I was punished for not castling and it is not actually a bad game for illustrating the necessity of castling. As always, your comments and opinions are welcome.
You'll notice that I muse about e3 - it would have saved my c pawn on move 12 if it had been played earlier and would arguably have saved the game by allowing me to move my bishop and then castle.
Also, my supposed pawn winning combo did not win a pawn at all, but hey, you can't fault a guy for trying.
Other than that, I think my trade on move 13 was a poor choice (yes I thought I could win a piece) as my bishop was my most active piece.