My name hasn't changed properly

Hello today I wanted to change my name from _Lenny to XX_Lenny69_XX , so I went on the minecraft site and changed it. On the Minecraft website it says that my name is changed but when I opened my minecraft launcher it stayed _Lenny . Now every time I want to acmes a multiplayer server it says that it doesn't recognize my name and doesn't let me in. Please help me as soon as possible. Thank you