Being unconfident and being a "nice guy" are two totally different things. Nice guys have weak boundaries, and engage in manipulative behavior to get what they want (i.e. appearing to be nice, sweet etc. with the implicit expectation that they will get something in return). Whereas lack of confidence is simply a lack of trust in one's self to accomplish the task at hand.
Based on your description, you lack confidence, you're not necessarily a "nice guy" (although you could be both). Building confidence is not a matter of trying to appear confident when you're not. That doesn't work. Rather, its about building up positive reference points. Do that enough, and confidence will naturally rise. What Chase means when he says you need to do things you're uncomfortable with is that you need to try new strategies. Some of them won't necessarily feel right or comfortable. This I NOT the same as trying to fake the appearance of confidence. Don't do that.
So to formulate it more clearly...building confidence is simply a matter of going out, doing something related to the task you want to be confident at and recognizing the fact that you were successful. Rinse and repeat.
In the context of picking up women, this might be something as simple as going out and saying "hi" to a women then walking away. Or, if you already know girls, going out and having a great conversation with one of them.
Its important to note that you must recognize these small victories as successes in your mind. A lot of guys go out thinking "Oh..well I didn't get laid so I failed.". This is far from true. Especially for beginners. Anytime you did something you previously wouldn't have or couldn't have done, understand that this is a success, and you must recognize it as such.
My mindset: i genuinely believe that I'm a guy who deserve girls and whom they would enjoy to be with.
This is fine, I'm not telling you not to do this. But understand that you can't think your way into confidence more than you can think your way into feeling satiated when you're hungry. The only way to truly feel confident is to go out and get reference points. Just remember that.
