You should have been charging on the low side not the high side. But it's actually good that you weren't able to top off the system. You should never use that stuff in any car AC system and it's outlawed in the states. This is a flammable refrigerant!
From the SDS (Saftey Data Sheet)
AUTO – IGNITION TEMPERATURE: 1585 F
FLASHPOINT: -34 C
LOWER FLAMMABLE LIMIT (LEL): 1.9%
UPPER FLAMMABLE LIMIT (UEL): 8.5%
From their directions:
Although RED TEK® 12a is compatible with most existing refrigerants
and oils, DO NOT MIX REFRIGERANTS. Mixing refrigerants is illegal in
Canada and the US and will not offer the maximum performance available
from RED TEK® 12a.
RED TEK® 12a Refrigerant is installed through the LOW SIDE SERVICE
PORT AND IS CHARGED AS A LIQUID INTO A "0" ATMOSPHERIC CONDITION. DO
NOT INSTALL INTO A SYSTEM WHERE A HARD VACUUM EXISTS. DANGER!! DO NOT
INSTALL ON HIGH SIDE SERVICE PORT.
Had you have topped off your system, and then taken it to get it repaired somewhere they would need specialized equipment to recover what would now be a blend because you mixed different types of refrigerant. Most shops just won't work on a car with a blend because it takes a machine just for recovering blends and they have to pay to dispose of the old blends because they can't be recycled or reused. So the shops that do have that equipment charge a lot to work on them.
If you are going to DIY AC recharge make sure you get the correct refrigerant (IE the exact kind in your car) and read the directions completely before attempting to do the repair yourself.