If you have difficulty hitting or triggering elements with your gaze, you may have an inaccurate calibration. This means that your viewpoint is shifted on the screen and is detected incorrectly by your eye tracker.
We recommend to repeat your calibration in such cases. In most cases it will improve the inaccuracy.
With Tobii you can activate the so-called "Gaze Trace" for a quick test. The Gaze Trace shows you your current point of view visually. You can also test your calibration in your profile and then improve it (see following figure).
Please note that Tobii's "Gaze Trace" may differ from your current viewpoint if NUIA's "Offset Compensation" is active. Instead, please use the visualization of the NUIA gaze point (tray menu < Developer Tools < Show my gaze).
After several calibrations you still notice a very high inaccuracy of your viewpoint on the screen, you can also try to have only one eye (left/right) calibrated for your eye tracker.
This is also possible with Tobii. You can select your desired eye in the setup "test/improve calibration" in the lower left area and then improve the calibration (see figure below).
Please note that with some eye tracker models a visual impairment (from ~4 diopters, astigmatism, anisometropia, etc.) can play a role for an exact recording of the eye data.