new to pacman frogs

[DVirginiana]

That tank is okay for a baby, but you'll need a larger one soon. A 10 gallon is enough for an adult, and a 20 is even better but not really necessary. Sometimes very small ones get intimidated by that large of an enclosure, so it might actually be good to wait till he gets a bit larger to upgrade him.

Where are you measuring humidity at? You should be measuring it right above the substrate; get much higher and it reads like... exponentially lower than it would on the frog's level. Their ambient humidity can drop out of the recommended range by a little as long as their substrate is moist, but at 40, the substrate probably isn't moist enough to make up for it...
If the top of the tank is screen, you can cover half or 2/3 of it with clear plastic wrap. That'll help keep humidity in.

[manbeardpigbear]

Im good on tank size and Im fairly familiar with reptiles, im was mostly worried about the bloating/retaining water. ok hmm my hydrometer is all the way at the top of the tank so maybe my humidity is even better than I thought.

[DVirginiana]

Yeah, I figured that was the problem If the hygrometer was at the right place and still reading 40 it'd have to be really dry. Get it to the right place just to make sure, but I'd bet your humidity is in the right range.
They can retain water in a dangerous way, but that looks different. Like, you know how the look puffed up right before they shed? If they look like that when they aren't about to shed or puffing up because they're mad/scared then that's a problem. It's normal for them to hold enough water that they visibly shrink when they pee.