That is not a scary stand. As was mentioned before your build looks solid. I have put togetber many petsmart sold tank stands. most of them ARE scary. As was mentioned you can put some weight in the stand (sand bag, cinderblocks) tho dont feel it necessary, and you could try putting down a sheet of ply being that it is on carpet. It should be larger than the stand to be effective. Go from wall to 5-6" out from the front, and 8-12" out the sides. I did this for a couple stands and it helped the slight movement, as well as leveled the tank being it was on carpet.
That is a great looking stand, very professional looking. Dont screw it up with a bunch of 2x4's
Bear