I feel your pain. I went out the other day for my first solo ride and I was hurting. The legs and butt were willing, but the lungs were burning. I have got to get out of this bike shop job, it's killing my riding. Ride often and it'll come back. Warm up, and keep the balance between muscles working hard and herat/lungs working hard. You'll make it. I've got a little more time, first weekend in June, but I'm planning the full century.