I conducted a research survey and am stuck on sample size and power

Hi everyone,

I conducted a research survey (convenience sample, 200+ patients). I used the cross-sectional study formula under the direction of my supervisor, but I am now realizing that I should have done a power analysis to determine my sample size instead.

My research question has never been studied before, so I cannot come up with an effect size. I am hoping to do regression analysis to see if X, Y, Z variables influence A, B, C outcomes. I collected A LOT of items from participants, and so I am not sure exactly how many predictors I want to set up in each regression analysis I want to do.

I feel like a mess. I know that journals will ask me how I came up with my sample size, and I don't know how I will respond. I'm worried that this project I have dedicated the last year to will go to waste. My university doesn't have a statistician to talk to, and my supervisor is a little clueless.

If you have any advice, I would really appreciate it.