If your boat is a hydro, or outrigger, the "wobbling" (I assume you mean the boat bounces from side to side on the front sponsons?) is called "chime walk". There are several possible causes:
1) Could be hydrodynamic (one or more surfaces isnt in alignment with the other surfaces and causing the boat to become unstable at speed).
2) Could be aerodynamic (same thing except the wind is working on some exposed surface and is pushing the boat to become unstable).
3) Issues of weight, balance, and C.G.

The first two problems are usually not the cause (if you have bought a RTR model or it the boat has been correctly built), but if it was a kit and built (for example) without the hull being nearly symmetrical (same depths, widths, lenths etc), you will get unstable behavior.

So unless its a poorly built kit, you are looking at #3. Try measuring: 1) where the front to back balance point is; 2) where the top to bottom balance point is; and 30 the left side balance vs the right side. If you are experiencing chime walking, the goal(s) are to get the front to back balance more forward by moving/changing equipment mounting (or using weights) to keep the nose lower and flatter; try to get the center of gravity lower (may not be possible); and lastly, get the left side vs right as close as possible to splitting down the keel or center of the boat. These will help reduce your chime walk.

PS If you use weights to bring the nose down and adjust the left-right balance (if it isnt balanced), place the weights as far forward and low as possible. That way you can use the least posible weight and get the most benefit.