Sounds to me like you may need to pay a bit more attention to your "alignments" when uphauling
When uphauling, ensure that your board is completely "across the wind". We call this the neutral or "T" position. If you have the board completely perpendicular to the wind.
Pull your sail up until the foot is clear of the water.
Check the alignment of your board across the wind, and the alignment of the clew of your sail straight downwind and perpendicular to the centerline of your board.
Now step behind the mast with both feet!!!! This is very important, as you cannot start out directly on a beam reach unless you get the mast up to windward of the boards centerline.
Then pull your rig "across the board" so that the mast is now slightly upwind of your front shoulder.
Then sheet in by rotating your upper body from your hips about 5-10 deg.
Your board will sail away directly across the wind and you will not need to resort to things like radically tipping the rig forward or stepping way forward on the board.
It's all about the "alignments". If you pay attention to them, you will have far less issues getting underway on a beam reach.
If you do not get the rig up straight with the clew directly downwind, the board will do exactly what you are telling it..... it will turn upwind almost instantly.
When beach starting, Ken has given you some really good guidance, but I might add that you need to start with your board aligned quite a bit further downwind than you think becuase as you go up onto the board, the rig is going to turn the board upwind....so.... you need to compensate!