That weaving is normal for some boats at slow speeds. If you let loose of the steering wheel does the boat continue to go straight? If not your trim tab may need adjusting. Porposing is another problem. Make sure your boat is loaded as evenly as possible. With the motor down check the anti-cavitation plaste. It should be even with the bottom of the boat. If all that is good check these out. Nauticus SX Smart Tabs - iboats.com Yes they cost more than whale tails but they are far superior and don't add the stress to the transom that the whale tails do.
Fair Winds and Following Seas
Bill H. PTC USN Ret
Chesapeake, Va