US doctor called

I had my 36w ultrasound yesterday at 37w3d. The techs said everything looked good, but this evening I got a call from the doctor that looks at the ultrasounds, and he said I had to come in Monday right away. He said they needed better images of the bowel and kidney. He said not to panic, but they needed to see me on Monday. Of course, I am panicked now. If it was serious wouldn’t they have me come in right away instead of Monday? He said my doctor did know about it, and he may give me a call, but to be sure to go in Monday. Has this happened to anyone?