Pictures would help, the instability may be unrelated, as you may have adjusted the headset incorrectly (top cap first, then stem).

Basically, if you're trying to lower the stem, unscrew the top cap (functions different than threaded with a star nut), remove the cap, remove whatever spacers you have, pull out your stem, remove spacers below stem to achieve desired drop, reinstall all spacers + top cap

I'm not sure what you did, maybe you removed a spacer and didn't reinstall it above the stem?