First Grow...Weak Stem

This is my first grow and my plant is very healthy and full. The only thing is my stem at the base of the plant is weak because in the first 2 weeks of its life, my plant did not receive adequate life. Right now its being supported by some string. Any advice on making my main stem stronger?

A bit late for that now. Use a stake to support it.

Also have a fan blowing lightly on it and slowly make it blow harder as it gets stronger, dont knock it over, just make it seem like natural wind.

a cal-mag supplement may help too. My stems are always stronger with cal-mag.