I daresay a head tightened to a C note is too tight. Plastic heads don't "shrink" when tension is loosened. It may also be a "high crown" head. Do you see the capital letter "H" stamped in ink on the bead of the head, below the bottom edge of the tension hoop? That means a high crown head.

You don't give a measurement of the depth of your neck cut out for the tension hoop. But it looks normal in the photo.

The best path forward is to drop $25-30 on a new Remo medium crown head. Tighten it carefully (keeping it level) to a G note, G sharp, or A gradually until you find a tightness that sounds best to you. It's very rare to need B flat or B.

Good luck.

Once stretched is the crown of a head permanently stretched? Guess that's the question. Certainly if you loosen the nuts, the tap note will get lower as will the taughtness of the surface. But will the crown spring back and raise the tension hoop? All you can do is try. Definitely go back to one of the notes Dick suggested.

Or spring for a DrumDial and find the tension from 89 to 92 that sounds good to you. Maybe lower is OK if you like that, but going past 92 is pushing it I think.

Or get a medium crown head, though I think these were designed to work fine with a high crown head tightened to a reasonable tension.

It looks like you need a head with a lower crown. As Dick mentioned, a high crown head should have an H stamped in the model number, but that's not always the case. The hoop is not level because it's bottomed out in the neck notch. That's going to make the head have an uneven tension which won't do any good for the sound.
As Dick and Ken both mentioned, a stretched plastic head won't shrink back to where it was when it was new. It would be best to replace it with a medium crown head.

Loosen the head and tighten back level. If it still bottoms out, either lower the neck ledge or replace the head as said above. It also appears the neck is jammed against the tension hoop. If so, some sanding is in order to give some clearance there.