I think I’m running out of yarn. Not in general (perish the thought) but for this particular sock.
In this situation, it would be perfectly normal to: knit 1 full round, rip it out, carefully measure the amount of yarn used, and do the math to determine how much yarn each stitch takes. Then calculate the remaining number of stitches in the sock, measure the amount of yarn remaining in the skein, and do more math to see if you have enough yarn. Entirely reasonable.
According to my measurements, I should have about 26 inches of yarn left over. I’m confident in the math, but I’m not sure how good my measurements are as yarn is a bit stretchy (though I did measure 3 times and take the average). We’ll know soon. Even having measured and calculated, I know I’ll be eyeing the remaining ball with great suspicion the whole time.