Looks like you`ve been given some excellent advice on how to get rid of the marks there, but just to add from my own experience, give it a good hand polish afterwards as otherwise you will catch the swirlmarks in certain lights. I usually use the g3 faracela compound myself,but this can be a harsh compound generally used for heavy oxidising or after a respray,more commonly known as "mopping".I`m not that familiar with the products your using,but with the g3 you can use water,actually you MUST use water, which helps to avoid burning through (which i have done!!) and you use a fraction of the product. I`m assuming that the silverline product is not the angle grinder type, but rather the two handed buffer. If so, they are a lot more forgiving than the other type. After a bit of practice, you should have no probs getting rid of the marks. The only problem will be, that when you see how nice the finish is on the patch that you`ve done, you`ll want to do the rest of the car!!!