It is hard to say for sure without seeing the model and knowing what types of features you used to create the surfaces. But some general advice is that whenever possible try to use existing surface edges as selections for new features rather than sketch entities. With most surface features when you select an existing edge you can tell it to make the new surface tangent to the existing surface.
It is hard to say for sure without seeing the model and knowing what types of features you used to create the surfaces. But some general advice is that whenever possible try to use existing surface edges as selections for new features rather than sketch entities. With most surface features when you select an existing edge you can tell it to make the new surface tangent to the existing surface.