C :: RSA Implementation And N Modulus

I have to develop minimalistic implementation of RSA algorithm in C for an embedded device.

I'm doing that for two days but I have run into a problem. The N modulus is the limitation for the maximum message value to be encrypted with RSA.

For example theoretically RSA-1024 can encrypt/decrypt messages 1024 bits long but I still cannot understand how to choose p and q values to produce N == pow(2, 1024).

Is it possible to encrypt/decrypt 1024 bits long messages in practice if the N < pow(2, 1024)?

So far I'm getting the following results

Code:
Encrypting with RSA
d=15689981, e=21, n=16484947
In=16484942, Encrypted= 6074492, Out=16484942 (OK)
In=16484943, Encrypted= 5468920, Out=16484943 (OK)

[Code] ....