Why retaking the same tests stops working
The first time you take an official practice test, the score is a real measurement. The second time, part of what you're measuring is your memory. You recognize a passage, you remember that the answer to the circle question was 12, and your score goes up without your skills changing at all.
That's the trap. A student who retakes the same tests can walk into the real SAT believing they're at 1400 when their honest level is closer to 1300. A fresh test is the only way to know.
What a good replacement test needs
The digital SAT has a specific shape, and practice that ignores it gives you a misleading score. Reading and Writing is two modules of 27 questions in 32 minutes each. Math is two modules of 22 questions in 35 minutes each. How you do on the first module decides whether you get an easier or harder second module, and the harder route is the only way to reach the top scores.
So a replacement should do three things: use that timing, route the second module based on the first, and draw questions in the same mix of topics the real test uses. Math leans heavily on algebra and advanced math. Reading and Writing is spread across four areas. A test that's mostly grammar or mostly geometry will give you a score for a different test.
Where to get more full-length tests
StudyPebble's free practice test is built for exactly this. Each attempt builds a new form from original questions (not copied from official tests), matched to the real test's topic mix and timing, with the second module routed by your first-module result. There's no account and no card, and you can take as many as you want.
Treat any non-official test score as an estimate. Official tests are scored with data from millions of students, and no one else has that data. What a fresh adaptive test gives you is an honest read on your current level and which skills are costing you points.
How to use the weeks you have left
Don't just take test after test. A full test every week or two is enough to track progress. Put the rest of your time into the specific skills that cost you points. Drilling ten transitions questions in a row does more for a weak transitions score than another full test.
In the last week, take one final full test under real timing, a few days before test day, then go light. You're not going to learn a new skill in 48 hours, but you can walk in rested.