I suggest getting some tall leafy plant to but in the back right corner for your Betta. While the carpet will be beautiful, Betta's still have their own needs and he'll really appreciate the cover! You can do anything; Water Wisteria (Hygrophila Difformis), Temple Hygro, Hygro Temple 'Narrow', Ludiwigia Repens is one of my choice plants; easy and has good color too. Rotala Indica would be a nice plant as well, small leaves so you can have a nice jungle look in the back with the carpet in front.
I'm a big fan of carpet in front with jungle in the back which is like...all my tanks lol.
I highly suggest using Root tabs or Osmocote tablets to help your Starugyne Repens, they really appreciate the root food. Mine are in a soil based tank and are doing wonderful with that. Eco-complete is a great substrate, but it's still inert compared to soil which holds nutrients, all plant substrate are just mixtures of clay and such which have some minerals but the plants will still highly benefit from a root tab placed in there. Actually, I use Jobes plant sticks from walmart, the ones for house plants! I break mine into thirds and stick into the substrate, my Dwarf hairgrass goes wild for them! My entire 1.5 Tetra cube is a grass tank ^_^