Lisette Traveler Dress

I love Oliver + S patterns for kids so have been itching to try a pattern from the Lisette line.  With some time between contracts for work this week, I was able to make the Traveler dress (Simplicity 2246).  I wasn't disappointed -- the instructions are fantastic and the pattern well written.  I can't get over how professional this dress came out considering my lack of experience sewing adult clothes!

I wear a size 12 in off the rack clothes but cut out a 16 on top, graduating to an 18 on the bottom to leave space for my rather large rear end.  I think it was the right choice for my comfort level but it meant the dress was very sack-like in the middle and, when I added the tie, the material bunched up.   There was likely some type of alteration I could have done to avoid this when I cut the pattern but I don't have any clue what it might be. I added four fish eye darts (not sure if that is the right term) -- two in the front and two in the back -- it helps a bit but I would like to know the correct way to fix this for next time. 

The fabric is a linen-cotton blend I bought at 50% off from Fabricland.  My husband is not a fan, which is too bad because I ended up with enough left over to make skirt.