Topping is done to reduce the height and won't hurt in flower. The plant will continue to grow in flower and if you're running out of upward space, then you can cut the top. If those little stems start to grow what look like balls on them, those are sacks of pollen, which mean it's a male and won't produce THC resin. If that is your only plant and it's male, you won't get anything useful from it; unless maybe you can use the leaves but that won't be much for you. Females produce the white hairs that turn red or brown. That's the sex of this plant you want.