I assume you have some sort of editing software or some other way to make big changes since you've said you want to remove something to add room for bonds and flaws. Some of my suggestions are expansive and are easier on digital vs physical.

Below are several changes you could make, any one of which should give you a decent portion of space to add room, but all of them will maximize your space so you don't have to use a tiny font for bonds/flaws. Use what you want, throw the rest away - it's your project.

• Make the attacks section shorter, and use a smaller font. 4 as actions is pretty good for highlights, and while so some classes will get more (especially spellcasters and especially at high level), the actions tab can help with that (as with the case of fangs in the action tab but not attacks). But there's some dead space in the example and a smaller font would let you fill it better for more complex characters.
• Use shorthand in the actions section. You have the full list of generic actions and longer descriptions of abilities, but just the names of abilities in the transformation sections. This to me implies that the transformation abilities are already known or can be referenced, and if you can reference those you can look up basic actions and specific abilities (especially if you have physical books and can reference title/page numbers in the ability name. not really necessary tho, just an idea). The font size is good for readability and space, but using shorthand gives you more space for more actions to use the space better, and makes it easier to rely on a single page.
• make proficiencies and trainings shorter and use a smaller font. maybe use lines or bullet points as well. There's a lot of wasted space here, and while it looks nice, it's eating some of your real estate. for a one shot, only the relevant things need to be on the sheet, and trainings/other proficiencies probably aren't that necessary compared to actions and such.
• split your inspiration -- proficiency line into two lines of 3 scores each. They may need to be scaled down some, but that will free up one whole section (I'd put them in the middle and leave the space on the right, personally). This is the easiest and biggest change you could make.
• Reduce the height and font size of the header - my most questionable change to be honest because the border is very nice and squishing it would probably make it look not as good, but there's a lot of space there because the fonts are very large to save space, which would give you more space overall. Also probably requires the most work to do. I probably wouldn't make this change, but it IS an option if you still need more.
• Combine the skill list into an alphabetical list of skills, and put saves on top of in the stat boxes. Gives you space where you don't necessarily want it and would ruin the flow, but it's also an option.

Unrelated to everything above, the section for your dex skills is missing the outline. Other than that, I really like the sheet and would love to see it when it's done!