I ended up getting my dress off of StillWhite and got a great deal, but since ordering it 3 months ago I've lost about 10 lbs and 2" each off of my waist and hips. It doesn't look or fit bad, but isn't as fitted as it could be. I'm considering whether or not to get it altered, but I'm worried about having the size changed and then either gaining the weight back or losing even more weight. I wasn't trying to lose weight, but it happened, and I'm happy with the size I am now. I'm hoping to stay this size for the wedding, but don't want to stress about gaining or losing a few more pounds.
Dress with extra space pulled back

Dress as is

Amount of extra space I have

Do you think I should have the dress fitted? Is the difference enough to be noticeable? The material doesn't stretch, and I want to be able to eat, sit down, and dance comfortably. When I pulled back the extra material it felt like I could still sit and squat fine. However, I also notice when I pull back the extra material the dress seems a tiny bit shorter, and it's pretty much floor length with flats (a 1.5" heel from footbed to floor is about perfect) as is. Would altering the side seams cause the dress to fit any shorter?
The only bridal shop in our area will work on the dress, but they charge an additional fee for outside dresses and I'm worried my dress will not get prioritized since I didn't buy it from them. When I tried on dresses at their store they said they did a first fitting 4 months out and a second fitting 2 weeks before the wedding. Since my size has changed enough in just 3 months time to justify alterations, I'm worried that this timeline won't account for any further fluctuations in my size. The dress has already been hemmed (it's a bit shorter than I would like, but I can make it work) and has had a bustle added, so the only alterations I need are to the side seams to make it fit tighter. My dress also does not have any appliqués, beading, or other detail work that would make it overly complicated or time consuming to work with.
I did ask if they could do it in a shorter timeframe since the alterations are fairly simple, but have not yet heard back. I also found a seamstress in town who has good reviews on Facebook who I have also reached out to, but cannot fine any other tailors/seamstresses in the area who work on wedding dresses. My wedding is at the end of May, so a little less than 6 months away (and close to prom season), and if I end up getting the dress altered I don't want to pay a fortune for it and would prefer to have it done as close to my wedding as possible to ensure the right fit.
How far in advance should I get the dress fitted if my weight is fluctuating?
Help! I'm nervous and don't know what to do, and I'm worried about ruining the dress I got, because there is no way I'll be able to get a replacement at the price point I paid for it if something goes wrong. I also don't want to spend a lot on alterations and then not have it fit right.