How to let guard down around new people?

I’m having trouble being my full self around people I’ve just met. It takes me a long time to let my guard down, like, months. With most people, it seems like they know how to be themselves right away. I’m not antisocial or anything, but I think a side effect of my being homeschooled so long is that it’s difficult for me to be the person that the people closest to me know me as when I’m with acquaintances. I know myself to be a silly and fun person at times, but I feel myself getting stuck being this serious person all the time now. I guess maybe subconsciously I’m blocking myself because I’m worried of being embarrassed? I really want to be just me!