Gymboree’s Chapter 11 bankruptcy filing lifts the Fitch U.S. retail sector 12-month loan default rate to 2.7% from 1.7%, the ratings agency said Monday. Gymboree has had a high level of indebtedness since a 2010 leveraged buyout transaction, and the children’s retailer faced $1 billion in debt maturities over the next 22 months, as of March 14. Fitch expects Gymboree to emerge from bankruptcy as a smaller company after store closures, but facing competition from companies like Children’s Place Inc. PLCE, +1.75% and department stores. “Fitch is forecasting the [U.S. retail sector default] rate to rise to 9% by…