You can open the angle up more on that punch...But this is something you need to work on on the heavy bag, to learn your distance, to play around with the angle, and just in general figuring out the move you are trying to make. That is where you work out the details of angles (your foot positioning, in this case), balance weight shifts, and so on. How you set it up for example- is it a counter to what he does? Do you have to draw him into a certain action, or do you take the lead and create the opening?
Then you get in front of a mirror and then you can see if you are telegraphing it, and how so.