Smooth or simplify the cut line

In Shape & size → Cut line shape (die cut stickers):

• Fill narrow gaps: the line bridges small gaps (between words, or between parts of your design) instead of dipping into them. Gaps up to sets how wide.
• Smoothness: low follows tight curves closely, high rounds them off.
• Simplify: fills in the ins and outs, up to a simple rounded shape around your design.

Reset puts them back to the standard. None of them ever makes the white border thinner.