I understand that the enchantments are greatly changed by different factors but I don't get why the strength of my enchantments say one thing before I create it and another after I create it.

I am making an alchemy circlet
my enchantment level is 74, with 2 perk points in enchanter and and 1 in insightful
I used a grand gem with a grand soul
and no fortify help
my circlet said potions are 22% stronger before I hit x to create on xbox 360
but then said potions are 16% stronger after I actually created it.

why wouldn't It tell me the strength that I am actually creating?

btw I meant a guestion about enchantment, don't know how to edit the title

Are you sure it was a Grand Soul? The only thing I can think of is that its a Grand Gem with a Greater Soul causing it to be less than displayed.

That's what I was thinking

Are you choosing item and enchantment before you choose the soul gem because normally it will give you the strength of the enchantment based on the largest soul gem you have, so choosing a smaller soul gem will give you less strength on the enchantment the best way to find out would be to choose the soul gem before the item and enchantment to see how it effects it. The best type of soul gem to use is the grand soul gem filled with a grand soul

The size of the soul determines the size of the enchantment, not the size of the soul gem. It helps to choose the Soul Gem first, as then the game should tell you what the size of the enchantment will be with that selected soul.

I checked and all my grands gems are filled with grand souls, but now with all of the same critera that I stated above now I can only create 15% stronger potions circlet, but it's still 15% after I create it, I don't know what made it go down from 20% to 15%. I tried drinking a fortify enchantment and it went up to 16%.

My character level is 27 so with the number that I stated above seems like my enchanting is not increasing

How many enchantment perks do you have? The strength of your enchantments won't increase very much unless you take a bunch of enchant peks. Also the math for the fortify enchant potions is complex and I cannot even begin to explain it, but a fortify enchant potion won't have much effect unless you have a high enchant skill and a bunch of perks. You should check the UESP for the formula.