is 3A for the output or input ? - the motorcycle battery is 6A.
The max output current is 3A, given you give it enough cooling. That's the limit and if you were to need more current in the output then just go for one of those ebay/amazon/aliexpress 300w buck converterts which can go up to 8A (they already have a small heatsink but make sure to test it out before use).
There is also another 300w buck converter but with a higher current rating (smth like 20A)
But if all you need is like 2 A, maybe 2.5A if you push it, then this chip is good enough.
And if you wanted to build your own buck converter with high current capabilities, then just find the datasheet of the chips they use in their 300w models and continue from there. (The inductor of course will need to be bigger and be capable of handling that amount of current)