Do i have to touch in my oyster to change between central line and overground at startford station?

Basically I am traveling from Cutty Sark (DLR) to Hackney Wick, Cutty Sark and Hackney Wick are both Zone 2 on the London Under/Over ground lines, however I have to change from the DLR to the Overground at Stratford meaning I'm ping zone 3 but not stopping. My weekly Oyster is only Zones 1-2 so do I have to top up my oyster or can I touch in at the Overground bit without a problem?