The frog seems to be stressed out. Being a new addition, it will take time for the frog to adjust to its new surroundings. Most pacman keepers keep the enclosure simple. There are several ways you can do that.

The simplest setup would be the rock platform. Instead of using gravel, use a few large flat rocks that are smooth around the edges. This will provide access to a platform that allows the frog to leave the water. You can then decorate with pieces of baked driftwood. I do not recommend using gravel, as the frog can ingest it and may impact in its digestive system. The most common condition of impaction is called pica, very common with larger frogs and can be deadly.

Watch the diet. Large frogs become obese very quickly, once again can be a fatal condition. Pacman's eyes are bigger than their stomach. It is best to feed smaller items more often. As the frog grows older, feeding becomes less often. By 18 months of age, the frog should only be fed 3-4 times per month.

I suggest leaving your frog alone for a few days.
When I worked at the zoo as an amphibian keeper, I witnessed several frogs flipping over on their backs. I would come in every morning to clean the cages and see a whole bunch of frogs on their back unable to right themselves without my assistance - it was really a weird experience, but no one was able to explain the behavior