It can be very hard to get a between the chainstays kickstand to be snug enough to not move. I far prefer a kickstand that mounts further back and attaches to the left side chainstay and seatstay*. If you must use the type you have then a piece of 1/8" or 1/4" rubber between the kickstand and the bottom of the cyhainstays or plate will help keep the kickstand in place.

* the chainstay/seastay mounted kickstand has ther advantage that when off the bike you can lean the bike a bit to the left and turn the pedals. That is a great thing if you ever need to adjust a derailler or put on a thrown chain.

Cheers