Hi Daniel. This is a common problem, not only in aikido. These may not help, but give them a try.
1) Keep your eyes open
2) Breathe out when rolling
3) Don't imagine you are rolling, just tell yourself you are moving along a straight (horizontal) line with your body. (It's easy)
4) Practise, especially harder, longer rolls, to make the normal ones seem 'easier' in your mind.
Hope some/any of this helps