In a word, yes. But the most important matter is to have the person who is giving teh POA to sign and to have that pereson's signature notarized. The witnesses are not necessary but can be helpful if there is ever a dispute about the circumstances or capacity. Normally, you should have the POA filed of record in the county clerk's office. They will not accept it for recording without a notarization.
The trouble with buying or borrowing a form i sthat it might not accomplish what you want it to do. Since you have not said, and I have not seen your form, I can not tell you if your form will work. The charge for a lawyer to review it and your intention will be minimal and well worth paying.
Please be aware that a bank or other place is not required to accept your power of attorney even if it is notarized!
Some banks will only accept a power of attorney done on their form & notarized in their bank by their notary!
Why? Because some people do multiple powers of attorney & then revoke them claiming they were "forced" to execute them!
Therefore, if you have an express reason for executing a power of attorney, make sure that the person or company where you plan to use the power of attorney will actually accept your power of attorney!
Plus, be aware that the power of attorney can be revoked at any time. And, then end at the moment of the person's death! Therefore, when the person dies they are worthless!
If you purchased this form at an office supply store or from a company from the radio or television -- they are probably not State of Texas forms & are worthless!!!
The State of Texas has statutory forms -- use those!