I think you've done the right thing by putting the first temp in.
That's an awfully big difference for only a half an hour... which is why I don't trust it. It's hard... but when Charting, you've gotta fight the urge to make your chart look the way you want it to look, ya know? It's tough... we all have times when we wanna monkey around with temps or whatever.
I do have to say that I think you have a very nice looking thermal shift there!! Today's temp is plenty high... and the only thing that will confirm O is the number of high temps, not the height of the temp itself.
Best of Luck & Baby