TextBox font size more than 48?

No, 48 is currently the largest available font-size.

There are several options:

• Use images of the text instead -- images can be sized however you want

Or, if you need to show non-constant words, you could use one of the "font" systems that someone has made that uses an image of every character to display text.

• Decrease the size of the canvas.

48pt means the text is approximately 48 pixels tall. If you specified the size of the SurfaceGui to be twenty thousand, then it would only cover 0.24% of the brick, while if you specified it to be 100 it would cover 48% of the brick.