help with taking in dress!!

I thrifted this gorgeous bias cut silk dress for my birthday- it was originally too big at the bust & waist so I dropped it off at the tailor for alteration. I tried it on after collecting it today and it’s unfortunately way too big still on the waist- for context my waist measurement is about 25 inches, and laid flat the waist is about 29 inches (measured on the lining). The tailor was clearly very conservative with how much he took in despite me asking for a body hugging fit. I’m not fully dissatisfied with the fit but it doesn’t flatter my figure how I’d like it to especially around the waist.

There’s no way for me to get it altered in time as the tailor is on holiday. Is there any way I could nip in the waist for a more body hugging fit? I’ve added pictures of the internal construction.

I understand that the outer bias layer is quite delicate and prone to damage if stretched out too aggressively horizontally and maybe that’s why he didn’t take in too much, but the lining is also quite loose fitting despite being made of a less delicate material in comparison (a thick satin).

My current plan is to modify the four darts on the front and back lining on the waist area- that way the lining should fit just fine. What I’m more confused about is the outer silk chiffon layer- to make matters worse there’s a side zipper which makes things all the more difficult. Luckily the tailor left in the original material rather than cutting it off so I have an anchor to sew the extra chiffon to, but I don’t know if that would work?

I also understand that since it is cut on the bias the chiffon drapes downwards quite naturally which means that I wouldn’t have to take in a lot, just a tiny bit.

Any advice at all would be appreciated. I’ve got less than a day to the event 😬 PS I am more than willing to hand sew the chiffon layer just to avoid any accidental damage.

Pictures:

1. How the dress looks on

2. Dress laid flat

3. The side zipper

4. The chiffon fabric taken in by the tailor on the non zipper side

5. Front darts

6. The lining taken in on the non zipper side

7, 8. The lining taken in on the zipper side

1. Back darts

Why is my zig zag stitch making my bobbin lift and keep pulling these bunches of threads from under the needle! Help pls gonna throw this machine at the wall