First time growing, one plant, 1 week old

if it is an auto flowering seed/strain it needs no darkness and would prefer to live under 24 hours of light at all times like right now. Your challenge going forward will be height. I have found no one thing fixes the height problem but there are ways to get an extra inch here and an extra inch there. Starting with low growing genetics helps but is not absolutely necessary. Try to keep your temp as stable as possible and leaving the light on 24/0 will help quite a bit.

 

try moving ur light abit closer looks abit streched

 

or put some more coco/soil in ur cup to support stem. also dont know if u have a fan in the tent but they really help with strenghen stems.

also noticed you dont have a hood on ur light? you want to be focusing all that light down,

 

A couple things. Do not use clear cups for growing. Light kills roots. Next time use a colored solo cup. You can wrap it with some construction paper if you have or just pop that cup into one that isn't clear. Make sure that there are drainage holes as well.
Your soil looks pretty dense. You need a light aerated soil. Get some perlite and mix that into the soil. Between 30-50% is good. Cannabis needs a light soil so that it gets plenty of oxygen to the roots. And it also promotes good root growth. If the soil is too compact, the roots can't grow as well and you'll have a smaller root mass. The bigger the root the bigger the fruit.
Make sure that you don't over water. Water your plant. Let the soil dry out. Then water again. Don't get into a schedule. I've gone 3 days between waterings and then go a week before they need some more. The plant and soil will tell you when you need to give more. The purpose for letting the soil dry, is to make the roots grow and search for water.
Your growing an auto. Autos can be very finicky at times and become stunted very easily. Sometimes, they don't like to be transplanted or topped. Most growers start their autos in their final pots. Their vegetative stage is relatively short, so you want the most growth that you can get in its early stages. That's why a good airy soil is beneficial. I've grown only 1 auto with success, and that was a miniscule yield and a very small plant. I fucked up somewhere with it. Also lighting with an auto is, the more the better. 24hrs per day or 20 on 4 off are optimal for autos. I'd say that your plant is pretty far behind because of the compact soil preventing root growth. Since you are going to transplant, mix up some soil/ perlite ( but please get some quality soil. Not miracle grow or anything with slow release nutrients) and transplant into your final pot. You will most likely see a lag in growth becausey the growth will be under the soil till it establishes a good root system. If you are going to leave it in that cup for some more time, bury that stem. And when you transplant, bury it up some.
Good luck.

 

When I said, mix perlite into the soil, I don't mean in the existing cups. You can break the roots.

 

Well, now is the thing with that. Me, I personally would transplant. Some would wait. But if you are going to transplant, prep your pot.with the new soil/perlite. Hollow out a hole big enough to fit the existing soil but deep enough to accommodate burying the stem some. You could bury almost to your leaves. But again, this will most likely slow upper growth some, because the buried stem will actually produce roots. When you go to remove this from the cup it's in now, take a butter knife and go along between the cup and soil (as long as you don't see a lot of roots) to loosen the soil from the cup. Put your hand over the cup with the stem between your ring and index finger to support the stem. Tip the cup easily an push on the bottom of the cup. It should slide out. Do this right over the new pot. The closer you are, the less chance of mistakes happening. Ease it into the hole and fill in. Don't worry about breaking away the old soil . You'll potentially do more damage hurting the roots. Give it a good drink and patiently wait for her to do her thing