high and welcome to the world of cannabis cultivation grasshopper, lol.

...and it shows you've done some homework, not many noobs would
think to build themselves a cooltube so, kudos to you bro!

...now, in your post you say, 'I was so scared for the first few weeks that it was
growing too slowly. Does this look normal for a 4 week old from planting?'.

...and to answer that, i'd say first that your plant looks nice and healthy, whatever
you're feedin' it, it likes it, lol. ...and second, the reason it's so short is the
light your using is too blue.

you don't mention what the wattage is but i'm assuming it's at least 2x
65watts for a total of 130?

anyway, as a CFLer myself, i'd suggest you dispense with the cooltube
and go with the lower wattage bulbs which will enable you to mix the
spectra of the bulbs in order to replicate sunlight, as best you can.

...here's a couple pics of a couple of my CFL fixtures, which are filled
with mostly 23 and 26watt bulbs in a mix of 6500K and 2700K. ...if
you look around you'll see these light bars are commonly used with
great success.

keep in mind also that you aren't required to use the y-splitters, plus,
there are many other different configurations, including hard-mounting,
they don't have to hang from chains.