Hey! I've been active in the global lindy hop scene for a while now, and all I can say is try not to worry, and try not to internalize it when you are not asked to dance or when someone turns you down. In my experience, lindy hop scenes can be pretty tight-knit and can seem cliquey or judgmental, but usually the regular dancers are not intentionally trying to shut anyone out. They're just focused on their own good time: they're trying to dance with their friends, or that person visiting from out of town that they haven't seen in months, or to just chill and unwind. It's not being selfish or self-centered or anything, it's exactly what you're trying to do too! If they turn you down or don't think to ask you, it is almost never ever personal. As a follow, I tend to turn down a lot of leads that I don't know or that I haven't seen dance yet, and that's my choice to protect myself. While I believe social dancing is a give-and-take, I ain't got time to manage a jerky leader's energy flow so that my rotator cuff stays in one piece and so we don't end up playing bumper cars with every other dancing partnership out on the floor!
I know your friend was trying to help, but I don't love the "just smile and look happy!" advice either. I would suggest trying to get to know some people - chat with folks in the dance lessons, or other people waiting to dance along the sidelines of the social dance floor. Is there a bar at your dance venue? Even if you don't drink, buy a soda or a coffee or a seltzer water, and get to know the bartender or the people who hang out by the bar. I love lindy hop, but as I come from a modern dance and ballet background, I forget sometimes about the social part of social dancing, and forget that I have to be a friend to make a friend, as my dear auntie says.
Also, if I can be just a liiiiiiiittle bit catty... if your friends are young, pretty, fit, dancing in the follower's role (which is what I'm getting from the context of your post??? please correct me if I'm wrong!), and getting asked to dance all the time, the odds are pretty good that you don't want to be dancing with most of those leads and that, in the end, your friends didn't want to be dancing with them either. I love my scene and my community, but where there are young women, creeps tend to appear out of the woodwork, and they go for the pretty, young newbies.
Hope this helps and hope you keep dancing!