It could be as you suggest, that you picked up too many sts in trying to get all the dropped row back on the needle. Just make sure you're not consistently doing something like working two sts at the beginning of the row instead of one st. (Pull the working yarn down as you start the row, so that you can see the st at the beginning of the row. Don't pull the yarn up and over the needle because that makes the first st look like 2sts.)
The other thing that will help is to count sts when you finish a row. Putting in markers every 10-20 sts makes that easier. Then if you find an increase in st number you can fix it right away.