Your wrists will not be straight when you catch a clean, and that’s perfectly fine. Whether a lifter receives the bar correctly on the shoulders or not, the wrists will be bent backwards in extension, but a bar caught on the shoulders (with elbows forward and up) is supported by the shoulders, so the wrists - although bent - do not take any of the load. A bar caught with low elbows, however, cannot be successfully supported by the shoulders and is instead supported on bent - and usually painful - wrists.