Giridharan,
Thank you for your feedback and interest in the AWSWAF F5 Rules product.
We are routinely working to improve the F5 Rules product to fix coverage issues. Please feel free to provide any further details regarding the sample OWASP SQL/XSS you used.
Please note that the AWS Managed WAF solution only provides coverage against common and simple attack vectors, and is not meant to replace a state of the art WAF solution.