Lower than expected SG from extract kit

[GreenEnvy22]

While my all grain is still working away, I decided to make a quick extract kit.
I got a Muntons irish dublin style stout extract can, and 500g of their dark spraymalt, and 550g of dextrose. Also got 1oz of magnum (12.7 alpha) hops.

I boiled 3.5L of RO water, poured in the extract, spraymalt, and dextrose. Added hops via a mesh bag.
Boiled for 10 minutes, poured into fermenter bucket full of RO water. Topped up to just over 23L.
Took SG reading after stirring, 1.032.
I was expecting higher, buy maybe that extra 500ml or so watered it down?
So boiled a bit more water and added 300g more dextrose (all I had left) and 200g golden yellow sugar.
Then I was at 1.038, still a bit lower than I aimed for but will have to do.

Anyone see anything I did wrong that may have caused the low SG? or does that just happen sometime?

Measurements all with my hydrometer.

 

[RM-MN]

I boiled 3.5L of RO water, poured in the extract, spraymalt, and dextrose. Added hops via a mesh bag.
Boiled for 10 minutes, poured into fermenter bucket full of RO water. Topped up to just over 23L.

You didn't do anything wrong per se but the answer is in the red text. You have the same problem that many extract brewers have. The concentrated wort that you poured into the bucket is much denser than the water you poured it into and/or added later and it went right to the bottom. It is very difficult to get good mixing and your hydrometer sample was mostly just the water you added. If your kit showed the expected OG, that is what you got and the 1.032 is a measurement error.

 

[GreenEnvy22]

Ok, if that's it I'm happy. I did stir it but perhaps not enough.

 

[RM-MN]

It really takes a lot of vigorous stirring to get the concentrated wort well mixed with top off water. Since the amount of sugar in the extract is known and the amount of water you added to it is also known, you can calculate the OG and be more accurate than if you simply give it a quick stir. Most kits will list the expected OG and you can bet on that figure being very close to what you get.

This isn't so with all grain because one person's ability to get the sugars converted from starches and to further extract those sugars from the grain will not be the same as the next. Most recipes are written with a specific sugar extraction based on the brewer's ability. Your may not be the same.