Check your setup block to the slot that is cut in your stock. If it is not the same size as your router bit, it will throw the spacing off. It will be too tight or too loose. You can cut a piece of stock that size and use it as a setup bar. That way it will ensure a good fit. Cut some test stock, and adjust the bar until you are happy with the fit. Every time you make an adjustment, start over with fresh stock. If you make an adjustment and rerun the cut piece through, it will only cut on one side. It will shift the stock to one side. Once you are setup it will be fun!
To save the project, you will have to lightly sand each tab. Tedious and could taper the tabs. I do not know the size of your project, but it can still work. It is better than the spacing being too loose. I hope this helps. Others may be able to shed more light for you as well. Good luck, post some pictures when you can.