I think this is exactly what happens when you use a "standard" terrain. When you strech that it becomes jaggy. Try to switch to "procedural" and see what this changes. BTW, if you scale, of course you make everything bigger. You maybe need to work on the terrain function again and change the scale and/or altitude to correct the stretching. Balancing things is the secret, as mostly in real life (too)!

One day your ship comes in - but you're at the airport.