Can I not set text using a stringvalue? [SOLVED]

I keep getting the error "Attempt to index upvalue 'class' (a string value)" and I'm not exactly sure why. I'm attempting to set a TextLabel's text to a StringValue's value that is stored under a folder named "Stats" under the player.

local player = game:GetService("Players").LocalPlayer

local mainFrame = script.Parent
local class = mainFrame.ClassName
local AP = mainFrame.Attackpower
local SP = mainFrame.Spellpower
local DF = mainFrame.Defense
local RST = mainFrame.Resist

game:GetService("UserInputService").InputBegan:Connect(function(key)
    if key.KeyCode == Enum.KeyCode.C then
        if mainFrame.Visible == false then
            class.Text = player.Stats.ClassName.Value
            AP.Text = ("Attack: "..player.Stats.Attackpower.Value)
            SP.Text = ("Spellpower: "..player.Stats.Spellpower.Value)
            DF.Text = ("Defense: "..player.Stats.Defense.Value)
            RST.Text = ("Resist: "..player.Stats.Resist.Value)
            mainFrame.Visible = true
        end
    end
end)

What exactly am I doing wrong because I'm totally clueless on this issue.

I've tried changing line 13 to this:

script.Parent.ClassName.Text = player.Stats.Class.Value

But then I get, "Attempt to index field 'ClassName' (a string value)"