I can't believe scope creep with no amendment is even legal

On mobile so apologies for formatting. Quick background on my situation — any input appreciated.

scope creep with no amendment. I've been dealing with this for about 2 weeks now and the situation isn't improving ngl.

The contract was signed 8 months ago. I have a copy of the original agreement. The total amount in dispute is approximately $99,000.

Am I overthinking this or is this a real legal issue worth pursuing?

Just want to point out — the statute of limitations might be a factor here. In some states it's as short as 1-2 years. Don't sit on this too long.