Your sentence is good. The native can understand it. but the following is more natural.

Keep on going !

今晩は、今勉強中です。アメリカ人が日本語を学ぶのは難しいです。一人で学習しています。難しいですが、諦めません。

こんばんは！

You did well. All make sense to me. You can focus more on the difference of grammar structure between English and Japanese from now on. I know it would be a bit hard for native English speakers to get proper Japanese skills. At the same time I actually think English is such a difficult language for East Asian people. If interested, don't hesitate to ask me anything about Japanese. Keep it up.