Hired as an assistant product designer, given other tasks

Please help! I need advise.
I’ve been hired as a product design and development assistant, but over the past 2 months of my time here, I’ve been appointed some major graphic design tasks including ad campaigns and sending things to print.

Since it’s a small company, I do the best of my ability to do these graphic design tasks, but I feel my work is sub par in their outcome.

It’s become a budding problem and is causing tension for me. How do I let my boss know my expertise lies within industrial/product design, not graphic design, without sounding like I don’t know how or want to do the tasks appointed to me?

Recently I approved something go to print that ended up being terrible quality. It was beyond my knowledge, but I’m sure the blame will be placed on me…

In a small firm environment, you will be assigned to do anything. Sometime related to design, and sometimes nothing to do with design.
Whereas in a large firm, you will still do lots of things that might and might not related to design such as documentation and reporting status.
That’s the reality of design profession compares to school life.
Just think of it as bits & pieces of experience that will help you in a long run.

Printing knowledge is good to learn, if you have problem getting the right color, talk to the printer, they often provides good advice.
Ask questions and good luck.