You've gotten into unfriendly territory. You need a lot of power, and a puny little solar cell won't do what you need.
Your pump is rated at 750 GPH, which is about 12.5 GPM. If you look for water pumps in that range, you can find https://www.homedepot.com/p/FILL-RITE-12-Volt-1-5-HP-10-GPM-Portable-Fuel-Transfer-Pump-with-Standard-Accessories-FR1614/310528825 , which uses 1/5 horsepower for 10 GPM, or 15 - 20 GPM pumps which need 1/4 HP. So let's assume you need about 1/5 HP.
A horsepower is about 750 watts, so you need 150 watts. Worse, without a battery to provide peak (startup) power, you need about 5 times the run load for startup, so you'll need about 1 horsepower, or 750 watts from a pure array setup.
If you have your array aligned so it is pointing directly at the sun, your solar cell will put out something like 60 watts. That the advertising on your cell says 300, or even 20 to 100 means nothing.
So, since 750/60 equals 12.5, you need about a dozen more solar cells. 2 or 3 will not cut it.
Also, keep in mind that, for a minimal system, you CANNOT leave the array in a fixed position. If you have an array pointed straight up, when the sun is 30 degrees above the horizon you'll only get half the power you would when the sun is directly above. When the sun is at 45 degrees from perfect alignment you'll get about 70% of nominal power. Note that seasonal changes in sun elevation will have the same effect as time-of-day movement.
Another way to look at it is to pay attention to your startup condition. Notice that with one cell you get 0.19 volts. A solar cell which is heavily loaded behaves a lot like a current source. So, if you add a cell, you should get a doubling of voltage for this load. Under this model, you need about 60 cells to get 12 volts. Fortunately, this isn't quite true, since once the pump rotor starts to move the effective resistance starts to rise, but it does give you some idea of how underpowered a single cell is for this pump.
Fortunately, you only need about 25% of your solar cell power to keep the pump running, and you can provide the startup surge with a fairly small battery, since presumably you only start the pump once or twice a day. Not so fortunately, keeping batteries properly charged isn't always easy, so you'll need to do some homework there. In principle, you can get away with 3 or 4 extra solar cells, but if you're not willing to build a tracking mount, 5 or 6 would be better. Since you're buying from Alibaba, caveat emptor applies, and you should be aware that polycrystalline solar cells don't do well in terms of efficency for low light levels, which includes off-axis operation.