Here are few photos of the plant. Thanks for the help. Image link:

I have not had much luck growing cactuses from seeds, but that doesn't mean it can't be done. I'm impressed you got one seedling. You did something right! Despite my limited knowledge of seedlings, I do have two San Pedro cactuses growing on my patio, one of which is about 3 feet tall. So I have some knowledge of caring for this species. I think if you've gotten a seedling, it must be at least moderately happy, so presuming you don't encounter any other significant problems, I'd leave it alone until it's old enough to be transplanted. All things being equal, most cactuses generally do not need fertilizer, though there are fertilizers available that are specially made for cactuses. You can use those if you want, but follow the directions carefully. It's even a good idea to ask a knowledgable staffer at your store/nursery of choice about how best to use the fertilizer. A nursery that sells, or better, specializes in cactuses, might be your best bet, if you live near one. San Pedro cactuses are hardier than your Sonoran Desert/Mexican varieties, but if you have your San Pedros outdoors in Zone 4, I'd still bring them inside no later than the late fall. Fortunately, San Pedro cactuses are one of the best cactuses to grow indoors, provided you give them enough light. Like many other columnar cactuses, they like to spread their roots out far, so when you transplant, give your guy a pot that's at least as wide as it is deep. And although you want to water sparingly, San Pedros are much more tolerant than your average cactus of extra water, so if you get overly excited and water too much here and there, it should survive. But generally, like any cactus .... when in doubt, don't water. Let it dry out between waterings. And San Pedro blossoms are rare. As I mentioned, the taller of my San Pedros is 3 feet tall, and it has never bloomed. And I live in Zone 9! (Phoenix)

I'd slice you a new piece that is completely healthy; at least six inches long is a nice size. Let it callus for a couple weeks out of the sun, but outside. I'd use a plastic pot maybe an inch or so bigger in diameter than the base of your cutting. Fill the bottom half of the pot with some cactus soil, stick your cutting on top of the soil, then put a couple or 3 inches of pea gravel around the cactus and on top of the soil. Mist it regularly. It should root eventually but it might take some time and I would not be trying to root it in an office. Fresh air, bright natural light is better. If your plastic pot is unstable, put it in a bigger terra cotta pot and stuff newspaper around the plastic pot to make it stable. Although in this case the gravel should give you weight and you might not need to do this, this is not a bad idea to avoid accidental upheavals. In nature these columnar cacti fall over and lay on the ground. Over time new columns shoot up off the old column. Doesn't sound like you have a long enough column to try this, but you can see how it works and how much these want to root and grow without any human help. Some guy was trying to sell 5 foot sections of these on the local craigslist for 75 bucks each! Dream on. Anyways I have rooted cuttings of san pedros as described above. Good luck.

Are you watering it enough? I had a different cactus that was aborting the flower buds like this, and I found out I should have been watering more once the flower buds appeared...I tried it the next time, and this is what I ended up with... Christopher