I ride that route daily. Here’s what you do:

Use Google maps to find stops and routes.

When you get to a stop, look on the signpost for the blue square that has the stop number (ex: 1234). Text “GRTC 1234” to 228-27. You will receive a text back with the eta of each bus coming in the next hour.

Caveat: though the Cary/Main line used to run every 15 minutes, it’s now every 30 due to driver shortages. But some days they can’t get drivers for all of the buses, so that adds an element of unpredictability. Also traffic delays—especially around rush hour—can put things off schedule.

Most of the time things work well though and the text message will alert you if they aren’t. Sounds like you just got unlucky.