Well there are very very few people that actually ride at 30 mph some of them are kieth lyman, and randall harris, and they ride with a rope that is about 30 feet longer than yours. So unless you are the absolute best rookie ever, I would start by slowing the boat down to about 23 or so. The length sounds fine! Part of the problem might also be riding finless, but instead of putting them back on, try just leaning back a little more. Riding with out fins will teach you to edge better. I have been riding for a few seasons now and just took my fins off this season, and I might never go back!
Good luck and have fun!