英文字既用法

Wanna actually is the spoken short form of want to
similar to
"gotta" which is "go to"
"gonna" which is "going to"

As i said, these are spoken short forms, not suggest to use when you write.

When people speak fast, some syllables tend to be shorten or omitted.
it is similar to Chinese, when you say 乜野 fast enough, it turns out to 咩

so since wanna is want to, you do not use present continuous tense after to with a verb in front.

eg. I wanna go to Disneyland (I want to go to Disneyland)
I gotta go (I got to go)
I am gonna leave in 5 minutes (I am going to leave in 5 minutes)

唔可以架,,,你自已讀都怪啦
Eg: I wanna to buy some ice-cream.
I wanna to buying some ice-cream.

I wanna go to movie - conversation - no iNG
I want to go to movie.