I think it depends a lot on your business model. If you are still making a profit at this price it is very different than if you are charging less than your costs due to an error.

Since you seemed happy with this price before learning what competitors charge, I’m assuming it is profitable for you. In that case, I would stick with it.

In my work we’ve always had a focus on making the client happy and renegotiating at this stage I feel would leave a bad taste in their mouth. Since it is one client of many, since it is for a limited time period, and since (I’m assuming) you still make a profit, I would focus on the asset you are creating of a happy customer with future revenue potential.

You may want to have a talk to them about what a great deal they are getting and you hope you can get a testimonial or something. And you also may need to start preparing them to expect a higher renewal rate.

But as someone who has also been on the buying side, I would not be happy at all with someone coming back with a big price increase after that part has been settled.