"No, I'm fine. Thanks anyway." "Nein, es geht mir gut. Danke." "Nein, alles in Ordnung. Danke für die Nachfrage." "Nein, danke. Es geht mir gut." "Nein, danke. Mir geht's gut."

There are various ways to express this as for example: "Nein,Vielen Dank.Das ist in Ordnung." "Nein, alles klar, ich danke dir jedenfalls."

BTW, the usual answer to such a question is either "Nein, danke" or "Ja, bitte". Sometimes that is shortened to just "Danke" or "Bitte". If you don't use it that way, the following happens: Once I saw that a rather small built foreign woman trying to carry a very heavy suitcase up a flight of stairs. So I asked her if she needed help. She said "Danke". I was confused, because it looked like she really had trouble with the suitcase, so I couldn't understand why she refused my offer. So I asked again. She again said "Danke". Finally it dawned on me that she was thanking me for the offer, and not refusing it. I was very close to just walking away after the first answer, because usually I don't pressure people into accepting help if they don't want it. That would probably have created a really awkward situation... So, don't use "Danke" in that way :-) At least say "Ja, vielen Dank".

Some options: "Nein, Danke, Ich brauche keine Hilfe." "Nein, Danke, mir ist gut." "Nein, Danke, alles ist gut."