I have a 300 gallon liner and a Beckett Pump with a capacity of 190 GPH with
a 2 ft discharge height; which is what I have.
Should I go with a bigger pump??

For smaller ponds, it's recommended to turn the volume once an hour or more.

That said, you might be able to get away with that pump. You could always
try it for a while. I'd say if it can be returned, return it, otherwise
give it a spin.

C//