You say you only planted it about 4 weeks ago, and the temperatures where you are have been high, reaching 80deg F in the afternoons, and that the Camellia does get afternoon sun.
This is a watering problem - the time to plant permanent, woody shrubs isn't in the middle of summer because its extremely difficult to keep the rootball moist enough. If you dug your plant up now, you'd find the roots were still potshaped, as they were when they came out of the pot, with no spread of roots beyond that - that means, although the soil around might be a little bit moist, that densely packed rootball is dry.
You have two options; if you have a hosepipe, leave the hose trickling at the base of your plant, very close to the branches at the base, for 4 hours or so, and thereafter, water the plant with several gallons of water every other day. Might sound like a lot, but watering the surface of the soil needs to be done sufficiently well to penetrate deep enough.
Alternatively (and this option is the one I'd recommend) carefully dig it up and soak it in a bucket full of water for a couple of hours, weighting the rootball down so its immersed. When you replant, find a short piece of pipe, preferably about 2 inches diameter, about 8 to 10 inches long, dig the hole for your plant, place it in position, insert the pipe so that the bottom is pointing towards the rootball and the top is sticking out of the top of the soil, at an angle away from the plant, and push the soil back in place round both the pipe and roots. Tamp the soil down, and water in well. Pour a gallon or so of water down that pipe every 3 days while the weather is still hot or warm, even if it rains - the only time you don't need to put water in the pipe is if you have absolutely torrential rain, but light rain makes no difference, you still need to do it. Once fall arrives and the weather is cooler and maybe damper, you can lessen the watering somewhat, stopping altogether as winter arrives.
If you don't have a suitable length of pipe, you can make do with a plastic soft drinks bottle, a larger one - leave the cap off, cut the bottom off and insert that in the same way as you would the length of pipe. Needs to be a narrowish bottle though, if you can find one long enough. Whether you use a bottle or pipe, that can be removed at the end of next summer, by which time (assuming your plant recovers at all) the roots will have spread out sufficiently well.