What a tutor actually does that you have to replace yourself
A tutor's real value is usually structure, accountability, and someone diagnosing your mistakes on the spot. None of that requires paying someone if you build it yourself: a written weekly checklist, a recurring calendar block that is hard to skip, and a habit of reviewing every miss the same way each time. The questions themselves are not the scarce resource, since the College Board's own question bank and Khan Academy are both free.
Build your own diagnostic
Take one full practice test under real timing. Score it by skill category rather than by the single overall number, and list every skill you missed along with how many times. This list is the single most useful thing a self-study plan produces, because it replaces the diagnosis a tutor would otherwise give you.
How to pick which skill to drill first, without anyone telling you
Rank your missed skills by frequency on the test multiplied by how often you get them wrong. A skill that appears five to eight times per test and that you miss half the time outranks a skill that appears once, even if you always miss that one. Work down that list in order.
Within the ranking, tackle skills where you already know the rule but keep slipping on execution before you tackle skills you have not really learned. The execution fixes are quicker wins and build the habit of finishing what you start, which self-study plans tend to lose first.
Running a practice session solo, end to end
Set a timer that matches real pacing for the section you're drilling. Do a small set, 8 to 12 questions, on one skill from your list. Grade it immediately against the explanation, not from memory. Write one sentence for every miss on why it happened. Decide whether each one was careless or a real gap, and note that skill's status before you close the session. Schedule a short repeat of that same skill in about three days.
Telling apart a careless mistake from a real gap, without anyone watching you work
Redo the missed question later, untimed, with no pressure. If you get it right that time, it was carelessness: a misread question, a rushed step, a sign error. The fix is a slower check on that question type, not more studying of the concept, because you already have the concept.
If you get it wrong again untimed, it is a real gap. Re-read or re-watch the explanation for that specific skill before doing more questions on it, because repeating questions without relearning the rule first can lock in the wrong method instead of fixing it.
Why full practice tests aren't a substitute for review
A full test measures where you stand; it does not teach you anything by itself. Taking test after test without reviewing the misses from the last one just repeats the same errors and burns time that targeted drilling would have used better. Space full tests out to roughly every two to four weeks and spend the time in between on your ranked skill list.
Free tools that cover what a tutor would
Khan Academy covers the content lessons for skills you haven't learned yet. The official College Board question bank has real, released questions you can filter by skill for extra repetition. StudyPebble is a free option built around the same skill categories, with a daily practice limit and an explanation on every missed question, which fits the short, targeted sessions described above without costing anything.