I'm halfway through and the proportions are clearly off

FIX IT NOW

1. Don't restart. Selection tool → Freehand → draw carefully around just the problem element
2. Three-finger swipe down → Cut, then three-finger swipe down → Paste. The element is now on its own new layer
3. Transform → Freeform (not Uniform — Freeform lets you stretch in one direction without affecting the other axis) → adjust until the proportion looks right
4. Merge back down. If the fix created a visible gap or seam, paint over it on a new layer with the surrounding color using a soft brush
5. For heads and faces specifically: if the entire head is wrong in relation to the body, it's faster to select the full head, move it to a new layer, scale/rotate until it fits, and merge back