Rcpp - Returning a pre-calculated hardcoded matrix with more than 20 elements

I am working on a function, which needs to return a 20x20 pre-calculated matrix of floating point numbers.

My code snippet below runs as long as I only enter maximum 20 elements, on the 21st element it fails with no matching function for call to 'create'. So, how do I upscale to the full 20x20 matrix with hardcoded values?

#include <Rcpp.h>
using namespace Rcpp;

// [[Rcpp::export]]
NumericVector get_pmat(){
  
  // Create vector
  NumericVector pmat = NumericVector::create(
    1.1, 2.1, 3.1, 4.1, 5.1, 6.1, 7.1, 8.1, 9.1, 10.1,
    11.1, 12.1, 13.1, 14.1, 15.1, 16.1, 17.1, 18.1, 19.1, 20.1);
  
  // Create a matrix, by setting vector dimensions
  pmat.attr("dim") = Dimension(5, 4);
  
  // Return
  return pmat;
}

// Run test
/*** R
get_pmat()
*/

Haven't run this, but by eye, it appears that it runs out of dimension.