It is normal to have low frame rates when you run 3DMark. It does not mean that there is anything wrong with your PC.
Benchmarks are designed to place a heavy load on your computer. A heavy load makes it easier to find the bottlenecks in your system. It also extends the usefulness of the benchmark by ensuring that it will still be relevant for future hardware generations.
Particularly in 3DMark, it is sometimes the case that only small differences in visual quality can be seen from very large increases in the amount of processing required when using the highest settings.