As others have said, keep an eye on your CB. If you have a typical DS 1, the handle will show you that the board has popped up. Also the tiller/rudder will feel very mushy, instead of more positive feeling.
As for the suggestion that the DS isnt as close winded as other classes, That is true. However, properly rigged and trimmed and sailed, there should be less than 5 degrees difference, even with the best one-design dinghys.
I sail often in the same start as many Thistles. Some of them 'A' fleet national sailors and boats. Over our typical 1/2 mile first beat, even the fastest seldom are more that 50-75 yards ahead of me. Usually when they try to sail over me, nearby, I can pinch and keep them back. And this is with my 19 year old 'club sails.
First you need a good CB shape. symetrical foil with thickest part 30- 40% from the leading edge. Same for the rudder.
Second you need to have barber IN haulers rigged for the jib sheet, to get the sheeting angle tighter to point higher.
Third, the DS is prettty wide, with very shallow CB and Rudder. Any heel lifts to boards out of the water, making them less effective.
Here is a link to a picture of the barber in-haulers on Lollipop. The pink line is the barber, and it is set at the distance that I use most commonly. Jib sheet is then tightened untill the aft edge of the sail is pointing at the spreader tip.
Other pics of how Lollipop is rigged can be found in the picture section. If you click on my name, and then click on 'personell galler of Phill' you can find all the pictures posted.
Hope this helps.
EDIT. Looks like Roger and I were typing and posting at about the same time. His comments about the main sail settings are the part of the equation I did not address. One slight disagreement however. Never sheet the main so tight that the boom is to windward of the centerline. Rule of thumb. Sitting in the boat, 1-4 wind, boom no closer to the center line than 12". Sitting on the rail, 5-7, boom nearly on the center line, vang to get the top batten parallel to the boom. Hiking, 8 +, Boom as close to centerline as possible until you are overpowered, then let it down again 6 - 12", vang to keep top batten parallel with the boom.
Many have tried using mid boom travelers to sheet the boom highter, and no one has found superior preformance with the boom above the centerline.