Hi Pat,
Here are a couple things to try. First, pick four segments at 90 degrees and add a pencil mark at the center of the outside edge. Now look from the top and make sure that all four of these marks are directly adjacent to the joints of the row being glued to. This only takes a few seconds and this alone will mostly solve your problem.
However, if you make your rings by sanding half rings, remember that you are working with an oval, not a circle, and depending on the amount of wood you remove, this could be pronounced. When you make your rings, make sure that you have a minimum of wood to remove to make the halves join correctly. If this is not the case. Stop and make adjustments to your sled to get this as close as possible.
Next, I have found it works best to have a stool (I'm only 5' 5") so that I can look down on the vessel from directly above the center. If you've marked the four segment centers this will make it easy to spot problems. As you add new rows, looking from the top makes it easy to look down the vessel and look at the joints on the row that is two above the new row and make sure that the joints are in line.
Next, the titebond glues have a quick set time which is good, but sometimes a little more set time will let you take a little more time to make adjustments. Until you get more comfortable with alignments, you might consider getting a bottle of Titebond Extend which gives you more set time. I have found that the the bond has cured in about the same amount of time regardless of which you use, but the extra set time can be a life saver. I almost always use Titebond Extend when I'm working with multi-generation laminations.
Others will have additional suggestions for you, I'm sure.
Lloyd