You can raise your Enchantment skill above 100, by using potions that increase your Enchantment skill.
To get the maximum possible enchantments you need to raise your Alchemy skill to the highest level. You can create Fortify Alchemy enchantments that will increase the effect of your potions considerably.
So you should first create a set of Apparel that gives you the highest possible bonus you can currently achieve to Alchemy. Use that set to create a batch of Fortify Enchanting potions. Now your enchantments should be stronger when you use the potions just before enchanting your gear.
You will have to do a few rounds of enchanting and creating potions if you're after the maximally possible effect. So, use your enchanted alchemy gear to create an enchanting potion. Then use that potion to create better Fortify Alchemy gear. Now you can use that improved gear to create a better enchanting potion, repeat until no more improvement is visible.
There are diminishing returns, so you won't be able to increase your stats infinitely.