Comment on a move

Hi guys, I'd love to hear your comment on a move I made in a tournament match (very poor players, if I myself scored 4 pts in 7 matches...). I played with black:

1. e4 e6 2. d4 d5 3. e5 c5 4. c3 Ne7 my goal is taking d4 pawn away, so I tried to give my opponent the illusion of a free pawn, but he spotted my trick :( 5. Nf3 Nec6 6. Be2 Looks like he's clearing his way for castling, so I played b6 7. 0-0 Ba6 trade baby, trade... 8. Bxa6 Nxa6 9. Nd2 and here come the "controversial" move.
I have the opportunity to win a pawn with 9. ...cxd4 10. cxd4 Nxd4 but I played 9. ... c4
I played like that because I hadn't castled yet and I'm significantly behind in development, so I'm not sure opening up the position is a good idea.
On the other hand, if I managed to close the position with c4 and keep it close with, let's say, b5, I perhaps have time to catch up in development and play a match with only dark square bishops, which is good for me and bad for my opponent. I also thought that, playing at a certain moment h6, I restrict opponent bishop even more.
Your opinion?
Thanks,
L.

His 9 Nd2 is passive: where is this knight going too? More active 9 Qa4 demonstrating your weakness on the light squares.
Neither your 9...c4 nor your alternative 9...cxd4 seem appropriate.
It is better just to complete your development: 9...Be7 intending 10...O-O. You are right that 9...cxd4 is not good as you have not castled and as you are behind in development, so the most logical way to proceed is exactly to complete your development and prepare castling.
If he plays 10 Nb3, then 10...c4 and you have gained a tempo.