If you have a new forestay and old shrouds, that'd explain your dillema. Several years ago the standard lengths were changed; forestays became a bit longer and the shrouds became a bit shorter. If you want your setup to work okay you'll either have to custom order another old-length (shorter) forestay or get new shrouds to match the new forestay.
I'd probably go with the latter choice as it's a good idea to replace the shrouds & forestay every few years anyway.