m = peripheral.wrap("back")
m.clear()
m.setCursorPos(1,1)
m.setTextScale(5)

local function centerText(text)
  x,y = m.getSize()
  x1,y1 = m.getCursorPos()
  m.setCursorPos((math.floor(x/2) - (math.floor(#text/2))), y1)
  m.write(text)
end

--Call function "centerText("")" to set text
--Use m.setCursorPos(1,y) to choose placement on screen

y2 = 1
m.setCursorPos(1, y2 + 2)
centerText("Admin Shop")