Welcome to the forum, onthehillgirl!
Your tension might have changed with the second sock. Or, you might have made the first sock with larger needles by accident. (I speak from experience...because I've done that before.)
Now, whenever I make socks, I cast on BOTH at the same time, and knit one row at a time on each one. This way, they both turn out EXACTLY the same. I'm a bit "particular" about my socks, I guess.