Rolling takes time for all ... except those who come from another art or are just naturally gifted. Some suggestions:
Use a good developmental pedagogy that allows you to develop your rolls without developing "bad habits"
Ask a senior student to work with you on rolls after class regularly
Spend the money on Donovan Waite's 2 Ukemi Videos ... they are an invaluable tool ... and pratice the variety of ukemi he presents
Spend some time focusing on the Uke side of Aikido ... when Sensei asks for questions, ask him or her how to PROPERLY take the ukemi for the applied technique
Best of luck!