Sparse coded multiple access (SCMA) has received considerable attention recently as a candidate multiple access scheme for 5G cellular systems. This letter proposes an improved uplink SCMA scheme where instead of the multi-dimensional constellation (MDC) mapping and a fixed number of nonzero elements per sparse codeword, a varying number of coded symbols from each user are directly mapped onto the resource elements. We show that the proposed SCMA scheme outperforms the MDC-SCMA scheme in terms of both error rate performance and receiver complexity when the user load is high.