The p/t chart for this car is in section 83-608 of the MB service manual.

If you are getting 58 degrees with windows up you're way off. If it is with windows open, which is the way that MB indicates in their charging instructions you are only about 3 degrees off. Since that is the only charging instruction I've ever seen asking for open windows, I expect that you have closed windows. In that case you are way off.

You need that other half can of refrigerant in there and a clear sight glass.

Good luck,