Violating the Objective of a Gambit

In this game I opened up with the Smith-Morra Gambit in reply to black's Sicilian's defense. The first dozen of moves were pretty much book moves.

However, the next following moves were disastrous. Move 15..Nb1 was intended to reroute the knight to be a blockader on e3 in anticipation of fire lines along the dark diagonal opposing my king. However, the knight got stuck at its home square (b1) until it reaches the end game phase. This situation happened prior to the strings of inaccurate move made by white starting from 16..Qd2. This shallow attack on black's unprotected d6 pawn was easily neutralized by 18..Rfd8. Then, all of a sudden, white's queen becomes ugly by being under a discovered attack and being a road block for the queen's knight journey. 

Better was sticking to the plan of running the queen's knight to the e3 square from which white could possibly look for a knight-bishop trade on f6 via g4. 

The next inaccurate move was 18..Rc2 with the idea of doubling up rooks on the c-file. Although it is usually a good idea to stack heavy pieces on an open file, in the game it was not the right time to do so. Black's knight move 18..Nd4 annihilated all the development advantage grip that white has. Trades were forced and white is downhill afterwards.

A lesson I learned was to focus on the objectives of playing a gambit. In this game, the Smith-Morra Gambit was intended to have a speeded-up development and and early attack. However, I lost focus during the middle game because of being dragged by some shallow attacks and tactics.

Because of making inaccurate moves, I started becoming quite defensive and completely deviated from avoiding trades. As trades occured, all the initiative that I had was gone and that simply ridicules the objective of playing a gambit.