Hi there,
If your reason for pinching off the tops on young seedlings is to gain more bud sites in the end, you're better off waiting until its bigger. Instead of cutting it, pinch the stalk in areas you want it to bend without severing it, let it droop there and recover...it will spread out more in a horizontal fashion.
What you're doing is actually slowing down progress. Especially when growing from seed, the plant simply needs to reach a certain level of growth before it's mature...and cutting it down at this stage only hinders that progress. (some may argue this)
In any case, a plant will naturally assign leader and secondary leader branches, essentially doing on its own what you're trying to do.