Check the side of the spool to see what your reel's rated for. If 20 lb is on the high end, you just have too heavy a line. If the middle range is 12 - 15 lb scaling your line down will make a world of difference. You can try walking it out and reloading, but I think it will still fly off. I use reels that take 300 yds + of 12 lb mono and I've found that spooling very close to the lip gets me extra distance, and wetting the spool with a sponge or something before opening the bail keeps line from falling off and helps it pass through the guides, gaining a little more distance. 12 lb casts further than 14, it all depends on what you're fishing for. A 10' med action rod, (my old Wonderod!) throwing 2 3/4 oz with 12 lb line goes maybe 75 or 80 yds on a good day, 14 or 15 lb may be more appropriate depending on your quarry or snags.