How can I make my baby feel secure and comfortable around others?

Practice. I would keep trying. Every baby is different. Some are more social while others need time to warm up to people. You can set up play dates or attend baby music classes. Just get out there and have fun. Let your baby follow your lead.
Let others know. Stranger anxiety is a normal part of infant/toddler development and some have more than others. If your baby seems to be very anxious around those she doesn't know, it is important to let friends and family know beforehand so that they can give her some time to get aquainted and feel comfortable. Keep her close to you and let others interact from a distance at first. She will feel safer this way.