getting back into shape

I am about 10 lbs over where I was last year, it should not be difficult to lose, if I stick with my plan of commuting to work at least twice a week, 3 yoga classes, and 3-4 bike rides, with the intent of getting to regularly riding the 50 mile ATC dam loop this summer, and doing something like 24 miles/ 3 laps at muleshoe or some backtrail on the greenbelt. The ATC ride this past Saturday was difficult -- I tried keeping up with the "A"'s for a little while but got dropped on a long uphill. And singlespeeding on the greenbelt last night was a bit painful as well - I got myself dehydrated and was suffering. Question for myself is -- should I quit rowing? I have not done it all year.