Congrats, Sigz. I'm a mechanical/aerospace engineer, though I didn't start in aerospace. The hardest thing about an engineering job isn't remembering how to calculate principle stresses or moments of inertia. If you graduated with a degree, you have enough basis to learn the idiosyncrasies of the company you are working for, and you will realize they are often very different from the theory you learned. The hardest part (for me at least) is time management, and figuring out "optimal" solutions rather than the completely accurate and correct solution (these take too much time). Also, if your company is ISO 9001 or something similar, much of your time will be spent on documentation.
So what kind of company are you with?