Hi, and welcome to community.rstudio.com! To help you get the right help for your question, can you please turn it into a reprex (reproducible example)? This will ensure we're all looking at the same data and code. A guide for creating a reprex can be found here.
Also, 300 parameters is a lot to simultaneously view in a correlation plot. You may want to consider paring them down or segmenting them into a series of smaller correlation plots, if that makes sense for your use case.