Two things. Op is taking this way too hard on himself, and the gf needs to be more grateful but is entitled to her opinion. Op did spend a lot of time and effort on his thing, and she should be grateful and recognize his efforts. But at the same time, if this thing he made isn't up her alley, she has a right to communicate to him that it was sweet of him, but she really was hoping for something more gifty.

Let's say for example your SO gives you a birthday present. Most people expect jewelry or a game they've been wanting, or that CD from an artist they like, or a record player, or something they've been eyeing up at the store and dropping hints about. People want something fun or interesting they can get enjoyment out of, or something they can show off, or something that shows you pay attention to what they like.

Now if your SO gives you a present and it ends up being something weird like macaroni art or a toothpick statue of Abe Lincoln, or a knitted sweater that doesn't fit right - it's kind of hard to digest that kind of gift. Yes a lot of time and effort went into it, but it is hard to really feel excited for something that just doesn't do much for you.

I am wondering if OP has done stuff like this for her before and never took the hint so she finally had to break it to him. There is no good way to honestly say you do not like something someone worked hard on, but there comes a point where you have to be honest and address it.

Hand made anything as a gift is risky. I suggest OP, if he really cares for this girl, take the criticism lightly and learn from it. Find out what she really likes and try to find that for her. Maybe next time combine something hand made with a second gift that is more her style, or try something traditional like take her out to a nice dinner and pick up some flowers. If you don't nail the gift, at least make up for it in memories and time spent with her to make her feel special on her special day.