[KWH]

The pass is legal.
Why? It met all requirements listed in 7-5-1, 2, 3, 4, 5 and 6.

Another spin on your play would be:
1st and 10 on the 50.
A1 takes the snap drops back to the A-43 and throws a forward pass to A2 who catches the ball on the B-40.
A2 then throws a backward pass back to A1 who catches the ball on the A-45.
A1 then throws a forward pass to A2 who catches the ball on the B-35 and then B2 advances the ball and crosses the B-Goal line.
Ruling: Touchdown for A

The is no limit on the number of forward passes that can be thrown in high school football. THE ONLY REQUIREMENT is that all forward passes be thrown from BEHIND the neutral zone.
Therefore both your play and my play are legal.

Hint: On both your play and my play I would keep my eyes peeled for Ineligibles Downfield because:
Table 7-5 #3 (Also see 7-5-12)
"Ineligible A players may not advance across the expanded neutral zone before the LAST pass crosses the neutral zone is in flight unless touched in flight by B in or behind the neutral zone".
Based on this, "Once an ineligible has gone downfield it does not matter if HE returns behind the line. If a "Legal forward pass" is thrown you will still have a penalty for "Ineligible downfield"!