I remember experiencing something very similar when first doing these, you probably lack the stability provided by the gluteals.
I found that I quite quickly was able to maintain my balance as I continued to train and my balance improved. Don’t be disheartened, drop the weight and focus on good form and you will be there in no time.
You could also try some glute activating drills like
Bird dogs and
supine bridges
(long time lurker, first time poster...)