Need some more advice on this desk.

So as it turns out, i cannot fit a 4ftx8ft piece of plywood into my car lol. just a little too wide. Anyhow, i thought it'd be smart to get a 3/4in 6ft x 20in and a 4ft x 20in pine boards. those did fit! However, after doing some researching apparently plywood is much stronger! do you think that this pine would be a suitable desk with 2x4 bracing underneath it?

here's a quick sketch of what the desk and bracing look like

http://imgur.com/NuQcFoV