***I 'have' (niepotr) organized A birthday 'acceptance' (nie rozumiem uzycia tego slowa tutaj, to nie bylo acceptance to bylo PARTY) 'to' ON Monday. (dni tyg duza litera).
...I organized a birthday party on Monday, tez mozna ...On Monday I organized a birthday party.
THE 'nice' (daj to pozniej) atmosphere 'was on acceptance not' (Nie uzywamy 'not' w tym sensie na koncu zdania)...(tutaj ..The atmosphere was NOT nice), AS THE 'visitors' ('guests '- na party to masz guests, visitors-w tym sensie to byliby 'niezaproszeni guests', wtedy uzyjesz slowo 'intuders') STARTED brawlING 'zaczeli-started'(dlaczego dajesz czasownik na koncu zdania?).
I have obtained (jak napiszesz I have obtained-to oczekuj co? a tutaj co? niema) 'by THE pestering visitors' (tego to nawet nie rozumiem).
...The atmosphere was not nice at the party, the guests started brawling and I had to throw them out.