Our swimming pool was installed last summer and we had the same problem when we removed the cover on May 2.
The "sandpaper" surface is caused by the new plaster leaching out calcium during winter storage. During the curing process, the plaster will naturally increase the ph of your pool water during winter storage and this high ph causes the buildup of calcium on the pool surface.
I purchased a stainless steel pool brush and used it on a daily basis for roughly one week to get rid of the calcium. Prior to completely balancing the pool chemisty, the calcium was very difficult to remove.
I did notice, however, that once the chemistry was balanced and the water temperature rose above 70 degrees, the calcium was easily removed even with my nylon pool brush.
The plaster surface in our pool is once again smooth.
I hope this helps.