Is yourself an demonstrative pronoun

No, the pronoun 'yourself' is a reflexive pronoun or an intensive pronoun.

When used as a reflexive pronoun, it 'reflects back' to its antecedent.
When used as an intensive pronoun, it emphasizes its antecedent.

A demonstrative pronoun takes the place of a noun, indicating near or far in place or time, previously mentioned or indicated by gesture. The demonstrative pronouns are: this, that, these, those.

Examples:
Mable, please make yourself comfortable. (reflexive)
Mable, I can't believe you made that yourself. (intensive)

Mable, I can't believe you made that yourself. (demonstrative)