I think one thing you need to have in your mind is that while it might be, it also may not be possible for you to reach 250W by August. Physiology doesn’t work that way, so don’t stress about the number and just put together the best training plan possible with the volume you can recover from. Don’t try and game the system. I personally would be Thrilled with another 10W by August - I’m in the race and racing too.
I personally would be using a Gran Fondo Plan. Low or Medium Volume, potentially a masters plan depending on the intensity you can take. I would back-date the start of the plan to whenever you started training. I also add Z2 Volume (Real Z2, not go out and have fun or crush it on group rides Z2) as I have time and can still recover from,
If you think your FTP is too low, then by all means just go schedule a ramp test, but know that those overstate FTP for some people. I like this as a good, productive Threshold workout that won’t kill you (Gray +5)
If it’s moderate or easy, your FTP is too low. If it crushes you or you can’t finish it, your FTP is too high. What you’re looking for is first interval manageable. But the last 5-10 minutes of the second interval solid HARD, but not Very Hard, Crushing, can’t finish it hard.
If you want to go to failure, look up the Kolie Moore Threshold Tests. Those will tell you if your FTP is set right, but are more difficult than something like the above Threshold workout.