3. Nf3 isnt terrible per se, but black should certainly be fully equal. Take a look at http://www.365chess.com/opening.php?m=7&n=34668&ms=d4.d5.c4.e5.Nf3.e4&ns=7.8.23.374.12646.34668. You have to take the epawn if you want to play for an advantage. In general, its said that the "best way to refute a gambit is to accept it." That said, 4. ne5 is the move that gives you a bonafide disadvantage.
But I want to focus on 7. qh5, as your exclamation mark is very very wrong, and I think this is where you can learn something. Yes, you win a pawn, but to do so you have to offer a queen trade with 8. qxd5. You seem excited about offering a trade into an endgame where you only have two pawns for a piece and give this an exclamation mark. Two pawns for a piece is generally a loss unless the pawns are advanced and/or otherwise threatening, and trading off your best attacker gets you closer to the loss. When down material, the general rule is not to trade material, especially queens, because the queen is your best attacker. Also, after qxq, pxq, pxp, pxp your two pawns for the piece are double isolated and quite weak. Easy win for black absent blunders. So very definitely something important to be learned here.
You were better off following up with your original idea of opening the light square diagonal with cxd. Your still not doing so hot, but it is looking like you do have some compensation, and, at the very least, there are a lot more ways for black to go wrong. Black gave you a gift by playing c5 instead of c6, and with cxd you can make it a chess game.
This time I went over it some