Hi, there:
Don't feel too bad.
I guess you didn't prepare much for iBT. The most important skill for listening section is note-taking skill. Barron's TOEFL iBT book is a good tool to learn this skill. Official Guide book can make you familiar with the format. Try these two books first. You will find a big change after these two books. Other useful books are Longman, Delta, Thompson, Cambridge etc. If you have enough time, go through all of them.