How to create left, right, and center frames with pack?

I have a left and right frame right now and tried creating a center frame but the problem is the left frame takes up more space and pushes the center frame to the right so any widgets I put in it aren't actually centered. Is there any way to make it work?

    self.leftside = ttk.Frame(self)
    self.leftside.pack(expand=True, fill=BOTH, side=LEFT, anchor=W)

    self.center = ttk.Frame(self)
    self.center.pack(expand=True, fill=BOTH, side=LEFT, anchor=CENTER)

    self.rightside = ttk.Frame(self)
    self.rightside.pack(expand=True, fill=BOTH, side=RIGHT, anchor=E)

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