Question
I recently bought a phalenopsis (I found two pictures which
looked like it where it was described as modest girl or hybride
but couldn't find any further information.) About a week ago, a
bud started to flower but it was still in the make-shift pot so I
repotted it shortly after, now, the new flower is starting to close
and the leaves are beginning to curl up. I know it was healthy
before I repotted it so I can only think I've done something
wrong. A few mistakes I know I've made are that I watered it the
day before repotting and then again when I repotted so it could
have had too much water, I wasn't able to find orchid compost
so used regular compost, and finally, I buried the only aerial root
(how serious is that by the way? should I take it out.) I'm
completely new at this and feel heartbroken that this beautiful
flower is dying at my hands, it feels like I'm doing everything
wrong. Is there a way to revive it? Please help.

Answer
Phalaenopsis Modest Girl is a registered phalaenopsis hybrid, registered in 1994 by the firm Floriculture.  You did not describe the condition of the roots at the time you repotted it.  They should all be firm with no "mushy" roots.  The presence of the latter, which need to be removed prior to repotting, could indicate that the mix was bad and repotting it was good (as long as any rotting roots are removed first).

Watering the plant the day before repotting is not a problem.  Hopefully, you used a commercial orchid potting mix to repot it. You can find it at most garden centers, Lowes, Home Depot,etc.  Orchid potting mix contains ingredients to facilitate air flow at the roots.  Usually it consists of fir bark, tree fern, osmunda, perlite, charcoal or some combination of these.  Potting your plant in a garden type of soil mix will lead to root rot and the demise of your plant so you need to be particular about this.

Burying the aerial root will do no damage as long as you have it in the type of mix I described. The plant may be showing sign of stress because there is not enough air movement through the mix that you used.

At this point I would not be concerned about the flowers.  You need to focus on establishing this plant in a favorable environment so it establishes healthy new growth and, only then, will it reward your efforts with flowers.