Help with string crossing while keeping fingers down.

Adult beginner here, about 4 months in, looking for some advice from the community. To start, I do have an in- person teacher and she's great, but there is one problem I'm still having.

When crossing strings from D to A or A to E depending on the lesson, there are times when I'm supposed to leave my finger pressed on the string I were playing while changing my bow to the next string. And for my life I cannot keep my finger pressed down on a string and produce a clear tone on the next string. My finger continually hits the next string from the top or side when I try.

Does anyone have any advice, either personal or links to articles/videos?

I haven't been able to find much on my own, probably because my terminology is wrong.

Love this sub, any help is appreciated!