First time cardigan maker

[LivS]

I am attempting making a cardigan and I am about halfway done the back panel but I realized it has stretched from 25 inches wide to 30 inches wide. I am wondering if that is going to be way to big so should I start over or just keep going. I measured the biggest part of my shoulders and they are 18 inches. I don’t know if this cardigan is going to be way to big so I should just restart or keep going cus it will be oversized but still fine. 

[Granny Square]

Welcome to the 'ville!

Stop and  do some measuring of your fabric in terms of stitches per inch - it sounds like you may have to consider what you have done as an oversized gauge swatch.  I've never measured my shoulders before, and I've sewn a lot of my own clothes for decades and that's probably not very meaningful.  If an adult gains or loses weight, their skeleton doesn't change., so the prominent bones at the top of the shoulder or whatever you are measuring won't help much with fit below the shoulders.  

Measure yourself (bust, waist, hips) if you haven't already, or lay out a cardigan you already own (that fits you nicely) on your bed and measure it across.  Is it 50"? (you mentioned it stretched from 25", so doubled would be 50")  Take the measuring tape and 'wear' it around yourself at the 60" mark - is this going to work for you?

Back to the gauge swatch.  Making up numbers for illustration, let's say you measured 20.5 stitches across 4" (yes, do measure partial stitches, tiny fractions of an inch add up to a big difference in fit).  That means 1 stitch is 0.195" across (4 divided by 20.5).  Now look at the pattern, and how many stitches across the back for different sizes--the back should be half of your sweater's body measurement.  The size you made ended up being 30", which would be 154 stitches.  Now look at how many stitches are across the back for different sizes, let's say another size is 140 stitches across the back, x .195 is 27.3" across the back, which is closer to the 25" it sounds that you were aiming for.  Repeating that this is all made up measurement-wise (but the math is correct for the made up numbers), it's just to illustrate how to answer your questions for yourself. (We can't know if x measurement is going to be too big or too small to your sense of 'it fits OK')

I have done that sort of thing many times, I always do a gauge swatch ahead of time and sometimes end up being 'off', so I do the math to decide it's either it's close enough for me to live with or I look at the pattern and follow the directions for a smaller or larger size depending on which way my gauge compares to the designers', and end up with a reasonable fit.

Edited August 7, 2020 by Granny Square