Hard to say whether your recipe approaches a 30% solution since it does not produce only sodium sulfides but a mixture of sulfide, sulfite, and thiosulfate.

Sodium polysulfide is not a definite substance but rather a mixture of sulfides, Na2Sn where n = 1 to 5. It can be prepared by dissolving sulfur in a sodium sulfide solution. This must be done slowly and carefully since the reaction is exothermic.