Fabric Puckering is typically caused by fabric being hooped improperly. Re-hoop your fabric without making it too tight and try your design again. For the best results when hooping, be sure to use the smallest hoop size that will fit your design.
If the fabric continues to pucker and the hooping is not the issue, it may be caused by using the wrong stabilizer.
Also, be sure to check your needle. A damaged needle may cause unwanted fabric pulls.