Mashing with full volume takes more space than boiling. So if you are planning to do a full volume mash in this 11L kettle for a 2 gallon batch, you will not fit it in there.
I'm going to just throw some numbers out, and you can use one of those calculators to see for yourself how it works.
If you want to end up with 2 gallons in the fermenter, factor in grain absorption and evaporation to come up with your total water. Let's say your kit has 4.5 lbs of grain. It will absorb about 0.4 gallons of water. Your small kettle on the stove, for example, may evaporate about 0.5 gallons per hour.
So you are losing 0.9 gallons during the brew. Add that to the batch volume of 2 gallons, and you have 2.9 gallons of total water required to brew the beer. That's essentially 11L. So even the water alone won't fit.
The grain itself will occupy about 0.36 gallons of volume in the mash. So a full volume mash for this situation will require 3.26 gallons of volume. You're way over.
If you reserve a small amount of the water - exact amount is NOT the least bit critical, just enough to make the mash fit without a mess - you can do a pour-over sparge at the end. After mashing, you would lift the bag out, place it in a colander placed over the kettle, and pour the reserved water over it into the kettle, rinsing the grains.
Then you'd be ready to boil. However, you will have about 2.5 gallons in the kettle. It'll be too darn close for most of us. Boilovers suck, especially on a stove. So you should probably withhold that water for AFTER the boil INSTEAD of doing the pour-over sparge. You would keep it cold, and just add it to the hot wort at the end to help chill it.
It is useful to work through the options using real numbers. I hope this helps a bit.