Three weeks to get some shape?

The next three weeks are going to pass anyway so you might as well use them to start working out again and improving your muscle tone. Will you be all the way there in 3 weeks? No of course not. Will you be in better shape than you are now? Yes almost certainly. I can’t think of any good reason why you would do nothing though and rely just on posture and clothes!

In my experience the two things which work very quickly to show visible results are 30 Day Shred done daily or Reformer Pilates done every other day. Joseph Pilates is famously quoted as saying after 8 Pilates class you will feel better, after 16 you will see the physical changes and after 24 everyone else will see them. They are expensive however.

Focus on glute workouts (squats, hip thrusts) and core exercises to improve shape and tone. Also eat enough protein, stay hydrated, and maintain good posture to look better for your holiday.

Good clothes and excellent posture. You can’t develop visible muscle in 3 weeks.

And a flat bottom etc is genetic. I’ve been doing heavy weight training for 8 years eating a good diet at maintenance calories and lots protein plus creatine but my bottom is still flat. I have very strong glutes but genetically a flat bottom.

Ditch a bikini and wear a flattering one piece or a tankini two piece - boy legs shorts can look really good and help flabby unconditioned bodies into a good shape.

I started Caroline Girvan's Epic programme and I could see muscle definition starting to show after 3/4 weeks. I"d lost weight but hadn't been able to exercise during the weight loss so was very untoned.
It was hard work, 5 workouts a week using progressively heavy weights, but I was amazed at how quickly I saw muscle on my arms and abs, and more shape to my bum/tops of legs.

Longer term sounds like you need to build muscle. This will help your boobs to some extent - mine have perked up since I started weights and got some pec muscles. Same with bum - squats, lunges and kettlebell swings will definitely help build a rounder bum (do build core strength first though to protect your back).

You should expect to get a bit heavier when you build muscle of course - I’m 5’3 and I weigh 9 stone, I weigh more than I used to (and ideally I’d lose 4/5 lb) but I’m much fitter and look more toned.

Not achievable in 3 weeks though! More like 3 months plus to see results. For now I’d start with Pilates/core as I said before and good supportive swimwear.

7 stone 7 pounds? How tall are you? Is it possible you would look better with a little more weight on… ?

Exercise wise you won’t build much muscle in 3 weeks - but doing Pilates may change your posture which always helps your shape look better. And it’s a good foundation if you want do weights without injuring yourself.

A good one piece with decent bum coverage and boob support will be your best bet. Lands End, Boden, John Lewis have decent coverage without being too frumpy IMO. Seafolly is a good brand too.

I have much the same problem after losing 5 stone. Its tankini time for me.
I think you need to be realistic. Choose swimming gear that will hide the worst bits.
Im busy at the gym but its going to take months.