Yep, I had a student that took even longer. Part of the problem was the fear of rolling - whilst everyone else was practising they were not able to get the confidence to do it. I ended up just doing a seperate ukemi class specifically for ukemis.
Make sure you can do the reverese ukemi well initially - this is much less dangerous. Try going from a reverese, straight back into the forward roll (since they are just the reverse of each other and it should keep your shoulder rounded).
Take it slowly in building up - but DO AS MANY AS POSSIBLE. If you are asked to do something you are not comfortable with, do something from lower (kneeling) - but do loads! The only way forward is for you to get used to your body turning round. Even if you are just doing normal forward rolls it helps.