If you have a lot of splashes when whipping, it could mean that your mix is too liquid.
Don't forget that the Chantilly will get firmer, even after you stop whipping, So it's not necessary to overwhip.
If you don't use all the preparation at a time, refrigerate it for later use. If it goes flat, melt and whip again.
To know more on this subject, see the publications and works of Hervé THIS, chemist and very good teacher, which explain all that you always wanted to know about this subject, and more besides.