In this context 'check in successfully', check in registered' and 'check in success' is not good English. I would say 'check in successful' if you want to use those words. If they are just logging into a webpage for their course then I think 'sign in successful' or 'login successful' would be even better. If you can use more words then my favourite is 'you have successfully signed in' or 'you have successfully logged in'. I would be interested to hear other opinions.

Registration successful