It seems you either did not get a date to take GRE or you don't have money to the test fee. Otherwise, there is nothing to worry about taking it once. There must be many so-so type of school which do not have a rigid GRE score requirement. In those schools, even if the Graduate School has some cut-off score, the graduate director or a professor can ask to waive that requirement if your application is strong besides the GRE score.