Welcome to the forum. This is a safe place to talk about your fears and worries.
I am so sorry you feel bad about yourself. I'm sure you know giving gifts to people will not make them like you. If they are your friends they like you for yourself, nothing to do with gifts. Sometimes being given a gift for no apparent reason can make the recipient feel uncomfortable and perhaps start moving away from you. The reverse to what you want to happen.
I am also sad you felt you had to say yes to something you were uncomfortable about and glad that has been sorted out. It does seem like you are very unsure about your self worth. I am certain you are are just as likeable and lovable as other people. You are trying to get over this and I congratulate you for writing in here.
Have you considered getting some professional help to overcome your self doubts? I can assure you that doing this will be useful. I know about self doubt and feeling worthless. I have felt this way for many years. In the end I became seriously depressed, quite unwell in fact. Not a good place to be. A good starting place is your GP who can advise on the best course to take.
I presume you are not at school. Do you go to uni? I ask because universities have their own counselling services. I am guessing you have a job which is how you buy presents for your friends. Do you have a particular friend who you trust? If you perhaps you can talk to them about how others see you. It's good to get an opinion from someone who sees you in a different light.
You said, I don't believe i have any worth despite all the reassurance in the world. I know how hard it is to get past this. While you are probably not depressed the black dog that haunts those with depression has probably been whispering in your ear. It reminds you how useless you are, how you do everything wrong etc. Not true. Your job is to throw this dog out in the street.
There is a thread in the Staying Well forum. It's called Talking to Your Inner Critic, Can It Be Tamed? Browse through this. It is a long thread so probably reading all through it may not be the best. Start a page or so before the last post. Join in the conversation and tell us what you think. Hopefully it will be useful.