If you click on the chart controls button in the top right corner, you can select or deselect the sampled query button right above the apply button.
Yup that's how you turn it off, but to be clear, running sampled queries as opposed to unsampled in necessarily a bad thing. If a warning light appears at the top saying the distribution is irregular, that may be reason to turn off sampling. If you're looking for results on a couple of very specific users or events which is a very very small percentage of your total distribution, then that may be a reason to turn off sampling. But most of the time, Interana's sampling algorithms are looking over a percentage of actors which reflect the distribution of the population very well, and it is running the query over those actors and then scaling. From experience, the results are super close to the unsampled results and the query is MUCH more performant.