I don't know how much my market worth is and am usually not confident of selling myself or giving a price, which is dangerous for a freelancer. Any advice on how I can get over this obstacle?

If you are new, I'd suggest you follow market rates or even go lower than market rates, just to get started and get some customers first !

After you had some clients, you will gain some confidence and you can accurately mark your prices based on your services and provided value.

Cheers!

I suggest network with people who are working in your field and ask them the rates they used to charge when they started out. Or if you are hesitant to broach the topic of money with them, maybe show them your work and ask how much they think it is worth.

Then raise your rates with your most supportive clients, be prepared to explain to them the rationale why. You just need to raise your rate successfully with one client so that this will be the new benchmark all other clients will have to accept.