Possibly. It's wired with fairly high gain, suicide biasing (hFE limited, through three transistors, no less!), and has terrible loop dynamics (a peak detector responds instantly and recovers slowly). Without any appearance of intentional compensation (perhaps the limited gain of the op-amps would be helpful -- doing it the bad way, throwing away loop gain instead of fixing the actual dynamic problem), oscillation or chaotic behavior (driven limit cycles?) should be expected.
Besides that, the waveform in general will not be sinusoidal, but rather flat-topped or lopsided (depending on reactance, and how slow the compensation is). This is because, if feedback doesn't change appreciably during a cycle (problem is, it does), the current flow is constant, so for a resistive load, it just clips the peaks.
There's also absolutely no current limiting, so calling it a "3A power supply" is misleading; it could potentially source much, much more, to its own detriment. (Even those awful Chinese (DC) bench supplies know better than to do that. Well, for a little while, until the bottom-shelf fan siezes or something and the whole thing wheezes the smoke away.)
How to fix it? The simplest way is also the best way. Start over from scratch. Build an audio power amplifier, and connect the input to a potentiometer on the power transformer. Voila, adjustable AC output. Boring use of an amplifier? You bet. Solid state control? Current limiting? You bet! (Assuming you added the current limit / protection transistors to the output stage, of course... you did, didn't you?..)
For bonus points, you can build the amplifier DC-coupled, and have a selectable input from three sources: DC (via TL431 reference perhaps?), AC (via power transformer and resistor), and external (via RCA or BNC connector, perhaps?). All of which go into a potentiometer (aka volume control) and the rest of the amp.
That's what I did for a bench supply. Difference being, that one started from tape drive parts. I mean rack mount, spinny reels, computery kind of tape drive. Not the full power, multi-HP kind, but a pretty good one nonetheless. Anyway, that had 20A+ darlingtons in it, and a 500VA (at least) transformer, good for +/-25VDC. So I have a 0-20V adjustable supply capable of short circuit current over 40A (measured!), which doubles for whatever kind of brick-shithouse-driving amplifier I might need (200W+ into one or two ohms, anyone?).
Tim