The finger is on the note — but is it in tune?

Knowing where a finger goes is not the same as playing in tune. There's no fret to stop you a millimetre short. So reading and intonation are separate skills — and intonation is the real work of this course for you, because it's built on the ear, not the hand.

The method: hear it, place it, check it

Three steps, in this order, for every note that matters.

Hear it first. Before the finger moves, have the pitch in your head — sing it, sound it on the drone, or play the open string it's related to. You can't land a note you haven't imagined.
Place it. Drop the finger where you think the note lives. Don't slide around hunting — aim, land, commit.
Check it. Compare what you hear to what you meant, and to something true: an open string a fourth or fifth away, or the drone. If it beats — a wobbling, pulsing sound — it isn't in tune yet. Move the finger a millimetre and listen again.

Checks you always have

The open string it matches. Your 4th finger plays the same pitch as the next open string up — 4th-finger A on the D string is the open A.

48 bpm

4th-finger A on the D string, then the open A. The same note — they should lock into one sound with no wobble. If the 4th finger sounds low (it usually does at first), your hand has crept toward the scroll.

A drone. Set it to the key's home note and play your phrase against it. In-tune notes lock in and seem to swell; out-of-tune notes buzz.
Resonance. When a stopped note is exactly in tune with an open string an octave or a fifth away, that open string rings on its own — a faint sympathetic hum.

48 bpm

3rd-finger D on the A string, then the open D below it — an octave. When the D is dead in tune the open string hums along by itself. Nudge the finger out of tune and the hum vanishes. (More on this in 'Ringing tones'.)

Your own ear, after the fact. Did that sound higher or lower than you meant? Name the error — "a touch sharp" — before you fix it, so the correction isn't a guess. Much more on this in "Hearing a wrong note".

Two rules while you learn where notes live

No vibrato. It smears the pitch and hides small errors from your own ear. Play clean and still until the location is solid.
Don't fish. Sliding around hunting for a note trains the hand to be vague. Aim, land, judge, adjust once.

Try

Drone on A. Walk slowly up the A string — B, C♯, D, E — landing each note, holding it against the drone, adjusting until the buzz stops. Then back down. Two minutes. This is the single most valuable thing you can do for your playing right now.