Hey Man first of all Welcome to grow diaries :) It's awesome to see yet another grower plant their head into cannabis cultivation. Here at grow diaries you will find hundreds if not thousands of growers willing to help out and share their growing experience. Now we all started somewhere and I certainly did not start off perfect or like alot of the growers I see on here.
Now your plant is looking really healthy but I must agree with the other growers here she is no where near where she should be in a matter of Bio mass for this stage. My eye I would say this plant is around 2-3 weeks old not 6.
Right thats my opinion now how can we change it. The above growers have all mentioned very good points which you should take into consideration. The general rule of thumb is this kind of set up.
The first thing you need to consider before even planting your seed. is air intake. This is probably the most important thing in our grows our plants need fresh air to grow efficiently By the look of your picture you have good extraction. Though may I ask is the extractor you are using only sucking the warm air out of your light ? If so you will need another to exhaust the hot spent and humid air from your tent.
Another thing you could do is change your light. as a grower above has mentioned LEDs are at their most technological advance stage they have ever been before with each company fighting so hard for your cash. it's not a question about more light it is the wave length the light is delivered and the type of spectrum the light has. HPS lights have a great spectrum for flowering plants but they lack alot of spectrums that LED lights can provide IE ir wave length's and the all important 3200k spectrum . This spectrums has proven its worth against hps bulbs over and over. When you consider the amount of electricity used in a hps bulb compared to LED and running times with most LED lights boasting over 10,000 hours of runtime compared to a bulb that can go at any moment alot of growers dont really see a use for HPS bulbs anymore. I have seen your looking at the mars Hydro ts 600 this is a great light and for your space I think it would be perfect. be sure to read instructions and hang the light at the correct distance when you get it. it may seem small and well nothing compared to the hps unit you are using but this will bring temps down dramatically. I personally use a ts1000 and my tent is 1mx1mx2m if you can afford it I would get that. though i am actually sponsored by VIPAR SPECTRA i can get you a better light with a heat sync for 15% discount pm me for more info.
Another thing us growers need to be quite strict with is the ph levels of the soil these should be kept within 6.5 and 7.5 I think don't quote me on that I'm a dwc grower myself. then the last important thing is water. Now like a grower has mentioned she looks like she has had too much and I would agree. Let her dry out and only water around the top of the plant do not water all of the soil or flush the plant she simply cannot take that amount of water it will slow her growth and also increase the chances of root rot. when the plant is large then yes saturate the whole media but at this stage she does not need much. You should only really add more if she is wilting most growers will allow the soil to become quite dry before watering again its a good sign the plant is taking up her nutrients or water as she should be.
Cooling is every growers enemy the heat can cause some serious problems when growing our plants obviously this is dependent on where you are in the world. some of the best ways include proper air circulation plenty of fans. IF you want a short solution you can freeze large bottles of water and place them in front of your fans this will only work for a few hours but better than nothing if its getting out of control. a humidifier can help control tempters but unfortunately you are at the will of mother nature and the air you intake though you can set your times that your lights are on to the night time hours of the day so that can be more control for you there.
Further to all of this your doing awesome for your first try. Mine went awfully wrong and died the first time but I persisted and 5 years later. Practice makes perfect with most things in life :) keep up the great work and go easy on the watering and she will surprise you :) the stain selection is a great one for beginners too barneys is a great breeder best of luck :)
Don't forget to select one of these as an answer if any of them helped :) Keep it green :) 👊