Just let er be. You're fing for now. If it drops below 148, then you may want to adjust temp by either drawing off some of the mash, heating it up and adding it back to the mash. Or just adding a small amount boiling hot water. Since this is a partial mash, I wouldn't be overly concerned with your conversion here, since most of your fermentables will be coming from your extract.
Not all chemicals are bad. Without chemicals such as hydrogen and oxygen, for example, there would be no way to make water, a vital ingredient in beer.