Probably, PSE is cropping your photo because it is not 4x6.
Normally, you need to crop the photo to 4x6 aspect ratio in order to print 4x6.
So, what are the pixel dimensions of this photo?
Use the crop tool. Enter the h & w in inches (4x6 or 6x4 depending on orientation), drag out the crop shield, then crop.. You need to do this before sending it to the printer.
Note: It is desirable to have the resolution in the 240-300 px/in range for printing. For web work, 72 px/in is ok.
Another thing, be sure to select the proper paper option in the print dialog, 4x6 vs. 4x6 borderless.
This photo at 1944x2592 is the wrong aspect ratio to print at 4x6.
As we have explained, you need to crop this photo to 4x6 aspect ratio, and then it will print without further cropping.