how do i be more likeable?

Stuttering can be overcome.
Speech therapists can help a lot.
But I would expect there'd also be free advice from specialists on line.

Being introverted usually means one feels tired after spending time with people and needs time alone to recharge.
Introverts usually like to have one (maybe 2, 3 or 4) very close friends,
and prefer depth and quality in conversation.
They tend not to enjoy small talk much - which is what most people engage in when they're chatting.

That said, our world is suffering from a pandemic of poor conversationalists - mostly due to Twitter and social media.
We do have a culture where far too many people think it's okay to talk over the top of others - too few people know how to really listen.
And many are too self absorbed to take an interest in others.
It's possible that your ending up feeling left out is perhaps their fault rather than yours.
You could try occasionally interrupting - perhaps when someone has been holding the floor for 10 mins or more. Maybe try saying something like, "can I interrupt? I'd really like to feel part of a two way conversation."

There's a book by Edward de Bono called "How to Have a Beautiful Mind."
It gives guidance on how to become an interesting conversationalist.