In an hour, I will be going to one of my Indonesian friends' house to help him prepare hot pots for his birthday.

My friend thought I was professional with it, however, I am not.

The use of "professional" here is quite unusual. Maybe you can say it more casually like: "My friend thought I did it like a pro, even though I'm not."

She won't disappoint us I believe.

This is grammatically correct, but a more natural way to say it would be: "I'm sure she won't disappoint us."

Hot pot is a popular cuisine in my hometown.

"Cuisine" is correct (like 菜系), but what you wrote in Chinese (菜品) is closer to "dish."

In an hour, I will be going to one of my Indonesian friends' houses to help him prepare hot pots for his birthday.

In this sentence, "hot pot" is an uncountable noun so you cannot make it plural. If you want to do that, you have to say something like "a pot of hot pot." Most people will just say "hot pot" though.

I realize that it is weird and kind of contradictory (e.g. "pizza" is both a countable noun AND an uncountable noun depending on how you use it) but that's just how I've heard people talk about hot pot.

My friend thought I was professional withat it, however, I am not.

"Professional with" is usually used when you are talking about being good at using specific tools. Example: "he is professional with his instrument."

"Professional at" is more common and is used when you are talking about an activity. In this case, the activity is implied to be "making hot pot", so it would be "My friend thought I was professional at [making hot pot]..."

She won't disappoint us I believe.

This is correct, but I think it sounds more native to say something like "I'm sure she won't disappoint us."

My friend thought I was a professional with it,; however, I am not.

This is fairly nitpicky of me, but technically, when you use "however" you should use the semicolon before it. Semicolons are slowly going out of style, though, and I feel like most native speakers don't even know when to use it. :D

As to the sentence, I think when you say "with it" you mean "making hot pot." Your sentence is fine; to be more fluent I'd probably write the sentence with a verb, such as "My friend thought I cooked hot pot professionally" or "My friend thought I was a professional hot pot chef..."

Or if you mean "professional" as in "really good at something," you could just write that. "My friend thought I was really good at making hot pot."

She won't disappoint us, I believe.

Just a little nitpicking by adding the comma there. :)