Is the dress yours or you’re borrowing it? If it’s the latter, ask the dress owner first. The last thing you need is her freaking out the day of the competition when she sees that you’ve changed something!
Now, if the dress is yours, I’d be a little scared of using safety pins unless they’re super heavy-duty, and then they’d probably be lumpy and more difficult to hide.
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How To Shorten Dress Straps With Safety Pin
Simply fold them over on themselves underneath the bodice and sew, then use a seam ripper to carefully take the stitches out.
This is a temporary solution that plant works. Safety pins can sometimes damage fabric Or… if you don’t take them out right away, some of the crappier safety pins leave a mark (rust-line) against the fabric. But either way, i would mention it to the friend first.
If it’s a borrowed dress, then make sure to take out the few stitches you will need before you return.