To be honesty i love your tank! Its great! Not to mention your gorgeous fish! that blue one is so handsome!
Only thing i can say is maybe try to get a taller growing bushier plant? Also maybe remove the sea shells, bettas dont live in salt water, so that may be throwing off the vibes....
I guess a background might work... but i have no experience with them, if you just get a nice bushy plant and let it grow in the background, you get a two for one! nice live plant and a great background :D
Also maybe try picking a theme?
I have some oriental type pagoda towers in my tank, i love asian history and art so i figured it be a good theme to do on my first tank :D
I just planted a Water Wisteria and it is supposed grow nice and bushy, so once that is almost to the surface i will remove the fake lily plant.
Moss Balls give a bit of zing too!
Maybe you can get some ideas from that :D
Hope we all helped!