OK, so the bus lane is well-marked and has the requisite signs, and you say you drove to the right of it. Their only evidence is a video of the event. You can normally view this on their website, so have you done so ? If you take them to London Tribunals, this will be the evidence they rely on, so it does need to show your car in the bus lane. Note that just being partly in the bus lane is sufficient for them to serve a PCN.