yeah, it can be, if your soil is hard to dig but 4" down is like half a shovel depth. I didn't have addy's shelf when I did my pond for the first time either and tried to cover the exposed parts with hanging plants, coco coir, etc but when I began to see other ponds I admired, they made me wish I'd known/done the same. So, you're getting that nudge now. Google pics of ponds and see if you begin to like the 'covered edged' ones better than the multitude of those where the edge liner is exposed. You're actually doing your pond a service too because the sun will break down the liner where exposed, and you'll get less life than expected.
Maybe have a fish n chips party where you invite some young, muscle-bound lads? The UK equivalent of a pizza party for unsuspecting friends and family!