Sounds OK. In theory it should be OK to use the present perfect for a very recent action relevant to the present; however, I've just done a couple of quick searches in corpora and I can't find a single use of 'just now' with the present perfect. I'm pretty sure an American wouldn't say it as they use it a lot less than the British. I conclude that yes, it's grammatically OK but might sound strange to American ears.
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