Wedding Plus One Dilemma

I am a chronically single, socially awkward 23 year old that got a plus one to a high school friend’s wedding in a couple months. I debated on going by myself, but my friends told me I could bring a friend with me to make me comfortable since I wouldn’t know many people there (everyone I know is in the wedding party so for dinner and cocktail hour and stuff I would be alone). The girl I was originally planning on bringing is a mutual friend that we had in high school who was the only one that wasn’t invited from our high school friend group. The more i thought about it, the more that I felt that would be awkward considering she wasn’t invited in the first place. This girl also happens to be one of my best friends so I feel as though I’m really in a pickle and am so afraid of hurting someone’s feelings, especially a person I care a lot about and see regularly. I had to give the name of a guest tonight since I had to RSVP and chose to take one of my other best friends. But now I’m panicking and feel that I made the wrong choice and am debating on just going alone or bringing my mom. Any advice on how to handle this situation and tell my friend this decision would be helpful. Any other perspectives or advice would ease my anxiety greatly too. Has anyone else been in a situation like this before?