I did get given a little bit of wiggle room on my 7-6, but a) that was quite a few years ago and things have since tightened up, b) I had evidence of having done well over 20 matches the season before and c) I had missed a lot of matches through a combination of a documented injury and a particularly wet winter. I had also done 2 or 3 more lines than required and my admin was spot-on (it hasn't been as good since!), so those factors probably helped - if I'd done middles instead of those extra lines, I would have met the requirements.
Honestly, if the end of April is your deadline, you should have time to squeeze it in. I managed to (somewhat accidentally!) do 10 matches this October, so it's definitely not impossible to get 20 in 3 months even if you haven't done a single qualifying game yet. It will require you to make yourself very available, but that's part of the deal if you're looking to double-jump.
I'd also strongly advise against asking for an extension at this point - with 3 months left, I think your RDO would legitimately be asking questions regarding why you've given up on meeting the targets already. If it gets to a week or two away from the deadline, matches have been allocated and you're looking to be a couple of games short, there may be value in sending in an email in documenting matches that would otherwise have got you over the line if the weather/covid had been kinder and seeing if it helps (so make sure you log these cancelled matches NOW). But doing it this far away from the deadline I think would come across as making excuses.