If you prefer to spend more time alone than you do with others, that is ok. It does not make you abnormal or wrong and it is not something you need to work to change, unless you feel called honestly from within yourself to do so, for reasons you alone can know.
To be a solitary kind of a person does not mean that you are destined to live a less happy life. Nor does it make you less worthy or valuable as a human being.
To say no, regularly, to invitations that do not appeal to your heart’s true nature does not make you unkind, selfish or unloving.
To give the best of ourselves we have to be true to ourselves. And for some amongst us, being true to ourselves means more time alone than most people can fathom. There is no better or worse way to be in this world. There is only the way that is true to you. And what is true to you is something between you and your own soul.