First of all, congratulations on your successful maiden! Judging from the video, I don't think it's tail-heavy. Being tail-heavy doesn't make a model climb; being tail-heavy makes a model sensitive on the elevator...and if it's too tail-heavy becomes extremely unstable and "porpoises" all over the sky. So it could be the incidences, but if those are as per the plan my first thought would be either engine power or possibly the thrust angle of the engine. ZERO thrust is fine. But make very sure there isn't even the tiniest bit of upward engine thrust. In fact, instead of adjusting the wing, you might also put a couple of washers under the top two corners of the engine mount. Of if the engine is beam-mounted on the VK design (as was common in designs of that generation) then place the washers under the rear positions of the engine flanges.
And yeah, I've never had a successful flight with the model hanging perfectly level. I always go nose-down.