There are two important requirements for determining whether or not particle tracks have opposite- or like-curvature, or even any curvature at all.

First, choose the X-Y plane, using the left-most planar alignment button in the event display tool:

Second, use shift+right-click-drag to adjust the magnification of the event. Like many graphs, to get a complete picture you may have to use several zoom settings, and the settings that make curvature clear in one event may not be the right settings for the next. So choose the X-Y plane, and as you move from event to event using the forward arrow you'll stay inside that same down-the-beam-line perspective. But zoom in and out within that perspective for each new event, until the direction of curvature becomes apparent. It may help to imagine spinning the tracks around the center until they most nearly line up on top of one another: would their curvature be the same, or opposite, once aligned? Spinning does not affect direction of curvature (clockwise or counterclockwise), so you can imagine the tracks aligning in this way in order to determine whether or not they are of opposite curvature. See this screencast: