Your problem is very common, and it is something that a person needs to deal with at some point in their career. The clever people get to it early in the way that you are.
Even at my level I find that the best approach to these situations is to position oneself as an educated person who knows a great deal of material from the books however is always willing to learn. The people of you will be doing this internship with have created a successful business through being practical and intelligent, looking for opportunities and exploiting them. They have far more runs on the board than I do and, of course, you.
The very best of these people also admit that they have never been classically trained in marketing. These people quite willingly bring you into their fold. When you retain your humility and say that you will only offer suggestions in the areas that you know then you are instantly a good operator.
The same "willing to learn" approach applies when you are in a product area that you don't understand. As an example I can tell you that Monica Orlovic left her undergraduate degree and began to work as a marketing manager for a company called Antelco which is irrigation equipment. Because she did not presume to speak outside of her areas of knowledge she was a hit with that company.
As far as being asked to technically do things that you don't feel 100% comfortable with, you will also be a winner. Your point about being computer savvy and easily learning is exactly the key to that door. You know a great deal more than you think you do. You are familiar with social media and content creation and many things that you consider to be commonsense will add value to the business of your company. But humility is important.
With many clients the bar is amazingly low. Stick with the basics:
- Who is the customer?
- What are they buying?
- What benefit do they receive from owning your product?
- How do new customers get to find out about you?
- Who else provides solutions to problems that your product or service solve?
About the company that you are going to do the internship with. The best way to describe them seems to be that they provide consumables to the heavy equipment market. That is a very good business to be in. A sales rep for Cavill (Caterpillar) can spend three to five years trying to set up a single sale which might net them a million dollars but there are lean years in the meantime. Your company's business is a dream because to generate income your company's customer needs your product. They cannot dig holes without buckets and tines and chains and conveyors or any one of dozens of products. The capital equipment sales are beautiful but consumables make the world go round.
At all points in our career we are faced with The Imposter Syndrome, where other people hold us in higher regard than we do ourselves. I know that you've got this, so prepare as best you can but then just go in and do your best. Your employer will be delighted.