Sixth-generation (6G) wireless networks introduce Integrated Sensing and Communication (ISAC) technology, enabling simultaneous communication and sensing through shared time, frequency, space, and energy resources. Designing ISAC waveforms is challenging due to the need to satisfy both high-capacity communication and accurate sensing. This work presents a dual-domain waveform design that integrates classical Orthogonal Frequency Division Multiplexing (OFDM) with a tailored sensing signal in the delay-Doppler domain with carefully adjusted power to enhance sensing resolution without significantly affecting communication rate. Moreover, the paper tackles practical challenges such as high sidelobes and decreased sensing accuracy due to underutilized frequency-time resources. To address these issues, optimal resource allocation over time, frequency, and energy is defined, along with a novel interpolation technique based on Schatten p quasi-norm matrix completion. Numerical results show that these approaches outperform current methods, demonstrating the potential for improving 6G networks.