Brother Henu gave great spiritual advice, and I know others will, so I'll give some material advice.
Self-esteem, while it will be affected by magick, can't simply be faked. You can't suddenly think you're worthy of this and good at that and gifted in the other, if you haven't lived through proof of this.
Confidence comes in positive feedback loops, so you should work to create these (workings might even push you towards these in many ways, maybe even my intent to write this is someone's working manifested, as they come read this and apply).
You try new things -> some success comes -> seeing proof of your success tells your mind you are capable -> you are then motivated to try more things -> you succeed more, etc.
This applies to magick, but it also applies to just about everything.
What makes you "worthy" or "deserving" is taking the first steps of these loops, where you try and push through not being skilled at something, and even fail, but not stop.
If you, then, fail less and less, and succeed more and more, you deserve the confidence that will give you, as you went and claimed it. Simple master morality.