Sorry, a, little late but yes, you can add hotter water to raise the temp but at this point conversion is probably well under way so it may or may not make a difference.
Are you using a calibrated thermometer? That will make a difference in your readings as well. Mashing low will basically give you a more fermentable wort meaning your FG may wind up being lower than anticipated creating a slightly drier, less sweet finish to the beer which may or may not be desirable to the style being brewed.
Nothing Left to do but smile and drink beer.....
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