over-egg the pudding

/ˌəʊvəɹˈɛɡ ðə pˈʊdɪŋ/

/ˌoʊvɚɹˈɛɡ ðə pˈʊdɪŋ/

to over-egg the pudding

to try one's best to improve something, to the point where one ends up ruining it