What is correct in this situation?

You answered correctly. In this situation, you must reduce your speed and the truck has right of way. The yield (give way) sign on your road means you must let vehicles on the priority road (like the truck) go first. Reducing your speed is necessary to be able to stop if needed. The truck does not have to wait because it is on the priority road. Always check for signs and adapt your speed when approaching intersections where you do not have right of way.