Great question! Both are used and can mean the same. If i say, 'i have to get out of here', that works and if i say, 'i have got to get outta here', that works. Outta means, get out of a place and get out can be a command and a verb. However, outta is not a command so in an argument for example, you wouldn't use outta as a command for someone to leave. I hope that answers your question. If you'd like to practice speaking, I'd be happy to help you develop a study plan. Feel free to look at my teaching profile and class offerings and send me a message if you think I can help you. Have a great day!