tds calibration

I bought some calibration fluid for my tds meter. Its made by hm so is my tds meter. The tds fluid is supposed to read 342. Im reading almost 500. I used a brand new sterile urine cup that I use for frags to pour the solution in. Can they be off that much. The bottle says 342 at 77 degrees. Its probably 60 in my room would that make it any different since they specifically say that temp it must mean something. This stuff is crazy expensive for what it is. 3oz of water with some disolv3d solids of.some sort. I paid $8 for 3oz of water.