During a sale is not always a good time for downloading, depending on the time of day and location you are at.

There will always be more data being transferred than the file size of a download, especially as bytes are checked and if any missing, repeated until downloaded okay.

It is also possible, that the 34 Gb is the compressed file size of the update, and you are downloading uncompressed files.

What does https://www.speedtest.net tell you, what kind of download speeds should you be getting?

You probably should contact GOG support. I recall reading that some antivirus or firewall software might be throttling or blocking Galaxy or GOG, and you need to make exception in them for GOG/Galaxy. I am hazy with the details as I haven't had such problems.

Another reason might be that the download server you happen to be connected right now is overloaded, but I think you should have seen some variance with the download speeds then, and generally I presume those download servers are run by Professionals(tm) who know what they are doing, and would increase capacity in case they are really running out of juice.

Is that your normal Internet speed, or do you mean that's the speed you're getting when downloaded specifically from GOG? What's your error rate look like? If you have a poor connection to GOG's servers, it's possible you're having to re-download a large amount of data due to high error rates.

thanks for the responses everyone. today gog had an update and when it restarted my download jumped from 6GB to10GB when the update was done and it relogged into gog. i ran speedtest and i get ping of 92 and 1.06 mb/s up and 0.76 down.
i live in the country so i have to use verizon wireless and i went over my limit for 4g so im throttled to 3g speeds . i dont have this problem on steam. when steam downloads an update for a game it finishes when it should at 1mb/s. oxygen not included update today on steam with a 50MB patch and it downloaded in less than 10 minutes .as for error rate i have no idea how to test that.