Simple summer dress for dds

[shivs1974]

I tried last night to make a simple summer dress for dd2 -tube type with shearing at the top. First lesson-do not make it when you do not have their measurements...so it's way too big. Can I completely (and I mean completely) unpick and resew ? Or should I buy more material and start again?
Either way does anyone know of a simple tutorial online? Couldn't find any...or maybe I'm not looking in the right places

can you take the side seam in both sides then cut off the excess?

Oh I don't think I'd know how to do that-thank you though for posting.
I started unpicking & unpicking -it's quite addictive-and have cut a bit off...will try again!
Do you know if I should back stitch the shirring or not?