When your punches are too close to eachother, your punch needle work starts to curl when you take it out of your frame.
You can fix this by steaming your project. Please note: you should NOT IRON your design, as this will permanently flatten your loops. Pin your project to a thin cloth towel with the loop side against the towel. Hold your iron about 1 cm (1/2 inch) above your project. Use the steam of your iron to damp your project. Allow the steam to completely penetrate the design, then allow your project to dry completely before removing it from the towel. You may need to repeat the steaming.
To avoid that your punch needle project curls in the future, follow the recommended space between rows and stitches. As rule of tumb your should make your punches the lenght of one needle diameter from eachother.
When you use a thick yarn with the wooden punch needle, the space between your rows should be slightly bigger. And when you use a fine refill needle with your clover embroidery punch the stitches will be very close to eachother.