If your sloppy joes mixture is too thin, then you can let it cook for longer to let the extra moisture evaporate. If you tried this and it is still too thin to serve, then you can combine a little cornstarch (1 tbsp) with cold water (2 tbsp) in a mug and pour the slurry over the pan while the mixture is simmering. Stir right away and keep cooking until thicker, which should take about 30 seconds. Repeat if needed until desired consistency.