Different frogs have different personalities. My first WTF was a little shy when I first got him but calmed down quickly. My second one that I just got recently took over a week to calm down but he's still rather shy. He still ate right off though. I'm assuming it's because he's young and needs a lot of food to grow. Since he's in a quarantine tank I was able to cover all 4 sides of the tank for a week so he could setting in and get used to the sounds. You might want to to something like that for a week or so. I don't think you need to remove the background, just make sure you cover the little gaps in the back so he can't climb down in.
Three musts for your set up:
1. Get a hydrometer. If the humidity is too high or too low the frogs will stress and may not eat. I like to keep mine around 60% during the day and it jumps to 80% sometimes at night.
2. The water in the dish has to be changed daily. Even if it doesn't look dirty, it is. When I change my frog's water dishes there's a slime coating on the plastic even if the water looks spotless.
3. Get some big bushy fake plants, such as ones that suction cup to the sides. They give the frogs somewhere to hide during the day. Both of mine like to sleep in the corners behind their fake plants. Although Glurmo sometimes sleeps out in the open.
I hope this helps. I wouldn't worry too much just yet. Oh and one more thing, I really like the fake grass on the log. It looks like a mossy log. Is it easy for them to climb on?