Service agreement out of focus

[zazou]

I am working directly for a client and after a few meetings I drew up a service agreement based on what I felt was necessary to work on as first steps.
After it being signed I coded away, some things suddenly had no importance and others were added.
Now about half of the original assignments have been finished along with couple of others not in the agreement (although discussed and agreed in emails).

I really want to clear out this mess and am wondering what the proper way to go about it is.
Do I suggest ripping up the first agreement and put together a new one? Make a new one with what is extra (but then what happens with items in the original that now have no importance?)?

What else should I keep in mind to minimise risk in my situation?

This project has no project manager and the client isn't very tech savvy.

[TykeMerc]

Nothing wrong with adding a "Change Note" to the schedule with new work packages exposed through the discovery exercise clearly implied by a non technical customer that engaged a tech specialist.

Just call the initial schedule a primary scoping piece or something.

[craig1]

There's nothing wrong with having a contract term that says you can amend. Here's a copy from my standard direct contract:

Schedule A to this Agreement can be amended by an authorised Officer from each Party agreeing in any written format, including electronic mail, to the changes. To be valid, any such change must clearly state that the intention of the change is to amend this Schedule, that both parties agree to the changes, and the date from which the change will be valid. A verbose log of all changes will be included within the schedule.