Might have air in the system. Run it up to temp with the radiator cap off to let air out. Should be filled to 1/2" above the top bar in the radiator.
As above and I don't trust shops.I'd go and get some cheap car coolant from the supermarket and make my own 50/50 with deionised water(Rain water or melted freezer water will do).You never know what they might have put in
You should change your coolant within every two years.Like oil,it gets tired.