Ok, while these guys seem they want to be helpful, two big problems.
One, you must get all the air out of the system before you attempt to add refrigerant. If you have air in there, it will interfere with the refrigerants ability to do its job. Do you have a vacuum pump?
Secondly, do those little cans have a high side gauge? What they don't. Well, you don't fill AC systems till the AC reaches a certain low side pressure, you fill it till you reach a target high side pressure. You also monitor the high and low side pressures to make sure that nothing is wrong and that it is behaving properly.
I really like those little cans at the part stores, especially the ones with the gauges on them, mechanics get to fix them all the time after customers have screwed them up by overcharging them, happens all the time.
You need three tools before you attempt your own AC work. These are a manifold gauge set ($65), a vacuum pump ($65), and a thermometer ($7). Thats a minimal set of tools worth $135 for cheaper versions. To refill a system that a DIYer has repair, basically to evac and recharge, usually runs between $75 to $100 depending on the system and amount of refrigerant it takes.
Furthermore, if you do it wrong, and air or moisture gets trapped in the system, it can cause internal damage over time, costing you expensive parts, like compressors, and other stuff you just replaced.