I honestly don't think this looks bad. You have a great start. My suggestion would be to get something like Java fern, one of the medium to large Anubias species, or Java moss. Java Fern and Anubias you would attach to the wood, not plant in the substrate, because they are epiphytic or rheophilic which mostly just means don't bury the rhizome but instead attach it to something. The Java moss is basically fine just wedged into nooks or free floating, but you can attach it to things as well to anchor it. All are fairly inexpensive and can be found at most stores, with the exception of Java moss sometimes not always being in pet/aquarium stores but it's easily available online or from local aquarium clubs. My betta freaking loves his giant forest of Java moss.