3rd wheeling friend

So I planned to go to Florida with my boyfriend to visit family and vacation, I brought the plan to my two good girlfriends friends and they sorta invited themselves. Now one of my friends dropped out leaving just one of my female friend to Go with my boyfriend and I. I want to tell her not to come since I don’t want her to feel like a 3rd wheel but she’s excited to go but don’t want to seem rude.