40 minutes is not a valid connection time at CDG from Aegean to United, and hence your ticket is not valid and should not have been sold to you like this.
The representative on the phone claimed it was?
I am assuming you are booked on A3610 arriving 11:05AM and UA914 departing 11:45am. This is the only UA flight each day, and there is no earlier connecting Aegean flight, so you will have to change it to an overnight layover (at your own expense).
The flight number is UA9848.
Did you book this directly with United or with a travel agent (or online travel agent)?
I booked it through United.com
If you leave it as is, you will most likely miss your UA flight and may not be re-booked since your connection is not valid.
The representative also claimed I'd be bumped to the next flight from Paris if I did miss my current flight. I asked how much the next flight from Paris would be, he said a few hundred dollars more, but he kept insisting that he thought I should stick with my current flight and I'd be fine.