I use Longman Dictionary to improve my vocabulary.
In longman, for 'wanna' it says as below,
wanna
wan·na /ˈwɔnə US ˈwɑː-/
a short form of 'want to' or 'want a', used in writing to show how people sound when they speak
I did not realize that wanna is sign of poor English before you told me. Thank you for your advice!