DataStore making all values into one?

So i made a article on this yesterday about saving the build. It worked (thanks guys!). But, there is a big flaw when the DataStore saves the data. It makes all the values I want to save in to one? So that means I can't load the build without it having a error because of the Position value I saved since it add the values up. How can I make the dictionary of values not turn in to one value? Here are the links to the scripts I have:

Save Script: https://pastebin.com/Y2W3kckk

game.ReplicatedStorage.SaveBuild.OnServerEvent:Connect(function(player)
    local partTable = {}

    for i, inst in pairs(workspace:GetChildren()) do
        if inst.Name == "BuiltBlock" then
            local position = {
                X = inst.Position.X,
                Y = inst.Position.Y,
                Z = inst.Position.Z

            }
            local material = inst.Material
            local color = inst.BrickColor
            local size = inst.Size
            partTable[i] = {Position = position, Material = tostring(material), Color = tostring(color), Size = tostring(size)}
        end
    end

    local success, err = pcall(function()
        BuildsDataStore:SetAsync(player.UserId, partTable)
    end)

    if success then
        print("Saved player build.")
    elseif not success and err then
        print("Not successful: "..err)
    end 
end)

Load Script:

game.ReplicatedStorage.LoadBuild.OnServerEvent:Connect(function(player)
    local s,e = pcall(function()
        local build = BuildsDataStore:GetAsync(player.UserId)
        for i, tab in pairs(build) do
            local block = Instance.new("Part",workspace)
            block.Name = "BuiltBlock"
            block.Position.X = tonumber(tab.Position.X)
            block.Position.Y = tonumber(tab.Position.Y)
            block.Position.Z = tonumber(tab.Position.Z)
            block.Size = tonumber(tab.Size)
            block.Material = tab.Material
            block.BrickColor = tab.Color
        end
    end)
    if s then
        print("Successfully loaded build!")
    elseif not s and e then
        print("Not successful: "..e)
    end
end)

Error when loaded: Not successful: X cannot be assigned to

Data that was saved in the block tables: https://i.imgur.com/WdY9wr1.png

Please answer my question!! -- DragonSpawner12 :D