I'm pretty sure you want to top it once it has about 5 nodes (someone who knows more should correct me if I'm wrong). I'm guessing you just wasted a little bit of plant energy by not topping earlier, but it'll still get multiple colas from topping now.
Just curious, so you're topping a plant that you want to make into a mother plant. I guess that makes sense, multiple main stems means even more branches. So do you think its better to always top plants you plan on taking a lot of clones from?