I thought that happened when the tree needs water?

Have you checked to see that water is actually making it to the roots? Sometimes, soils can be resistant to percolation.

Best option is to do what John says and check the soil with a wooden skewer for moisture or stick your finger down in the soil to feel if it's wet. If the soil is wet, keep an eye on it for another 2-3 days without watering it yourself. It should perk up by itself if the tree has no root problems. If it gets worse even though the soil is wet, that means the roots are damaged from too much water.

Curling is the equivalent of wilting in other plants, so it may just be the heat dehydrating the leaves. If it's dry, put a trickling hose underneath it for a few hours to saturate the soil. That worked for me when mine got really dry. Also, squirting some dishwashing liquid on the ground around it before watering (not grease -cutting) will act as a surfactant and help the water "stick" to the soil instead of just running through it.

It also looks like it needs fertilizer, though it is probably too late to add any this year unless you live in south Florida.