Prepared for 40 Hour Research Internship - Changed to 20 A bit of backstory- I'm a rising sophomore undergraduate student studying computer science who is strongly interested in urban planning as well. This spring, I put about 12 hours a week of work into conducting undergraduate research with a lab at my uni and was offered a funded research assistant internship with the same lab this summer.

As this is my first time getting a real job (outside of high school), I had assumed that I would be working full-time this summer without communicating with my professor that much. Obviously, this was wrong to assume, but I have since learned from that mistake and take full responsibility.

However, my professor recently wrote me an email saying that he expects me to be working 20 hours a week, even though I have worked 40 hours a week for the first week of my job. I contacted HR and they said I was down as a full-time employee, but that if my professor expects me to work 20 hours, then I should only work 20 hours. This is the first time we have ever really communicated about work hours at all.

To make matters worse, I had planned to write a paper this summer, but the timeline I composed had assumed I'd be working 40 hours a week. The paper's deadline is on August 1st, and I'm concerned I won't be able to complete research working just 20 hours a week.

I am really interested in working on this paper, so much that I am even willing to put in time outside of my job to work on it, if necessary. My prof is unwilling to negotiate hours with me until mid/late July, and I plan on getting another part-time job now. I'm also taking 2 summer courses (online and CLEP though, so not too bad).

Should I propose to drastically narrow the scope of my paper so that I can finish it with a 20 hour work-week, or should I bite the bullet and try to keep working on the paper as it stands outside of work (time permitting)?
As in 50% of the questions on this forum, the answer to your question is: Talk to your professor. He may have a plan and can advise you on how to proceed. Or he hasn't thought the issue through and talking to you about it will make him articulate what his expectations are and match them with the ones you will have an opportunity to elaborate on this occasion. Or he doesn't have enough money to pay you for 40 hours and that's just the best he can do. 

So many possibilities we all just can't know here but that a short conversation with the person in question can resolve!