Too small how can I fix it?

I am knitting a full body suit for a 2 yo. I’ve been at this for a whole year and now I have knitted everything but where the buttons will go and the neckline

It’s like this

http://www.sandnesgarn.no/mariusdress-og-lue

I was trying to work out steeking and adding the arms when I realized I have either decreased too much or my knitting is way too tight as I’m like 15cm too small in the chest area where the different Colour’s are.

How can I fix this? Should I just make the part where the buttons go bigger? Like twice the width? To try and make it big enough?

What are my options. Unraveling isn’t and option. I’m so over this project :confused:

I wonder if you could make the steek a bit longer and add a gusset (a V-shaped insert) to the sides in the chest area? It would have to divide at the sleeves and extend up to the shoulder seam on each armhole edge.
It’s such a sweet pattern but sometimes you’re so ready for it to be over. Alternatively, could you save this for a younger baby?.